Week2 cloud computing week2

CLOUD COMPUTING
Web Services, Service Oriented Architecture
PROF. SOUMYA K. GHOSH
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
IIT KHARAGPUR

2
What are “Web Services”?
“Software application identified by a URI, whose interfaces and bindings are
capable of being defined, described, and discovered as XML artifacts” – W3C
Web Services Architecture Requirements, Oct. 2002
“Programmable application logic accessible using Standard Internet Protocols…”
– Microsoft
“An interface that describes a collection of operations that are network
accessible through standardized XML messaging …” – IBM
“Software components that can be spontaneously discovered, combined, and
recombined to provide a solution to the user’s problem/request … ” - SUN
2

3
History!
• Structured programming
• Object-oriented programming
• Distributed computing
• Electronic Data Interchange (EDI)
• World Wide Web
• Web Services
3

4
Distributed Computing
• When developers create substantial applications, often it is more efficient, or even necessary, for
different task to be performed on different computers, called N-tier applications:
• A 3-tier application might have a user interface on one computer, business-logic processing
on a second and a database on a third – all interacting as the application runs.
• For distributed applications to function correctly, application components, e.g. programming
objects, executing on different computers throughout a network must be able to communicate.
E.g.: DCE, CORBA, DCOM, RMI etc.
• Interoperability:
• Ability to communicate and share data with software from different vendors and platforms
• Limited among conventional proprietary distributed computing technologies
4

Electronic Data Interchange (EDI)
• Computer-to-computer exchange of business data and documents between
companies using standard formats recognized both nationally and internationally.
• The information used in EDI is organized according to a specified format set by
both companies participating in the data exchange.
• Advantages:
• Lower operating costs
• Saves time and money
• Less Errors => More Accuracy
• No data entry, so less human error
• Increased Productivity
• More efficient personnel and faster throughput
• Faster trading cycle
• Streamlined processes for improved trading relationships
5

Web Services
• Take advantage of OOP by enabling developers to build applications from
existing software components in a modular approach:
• Transform a network (e.g. the Internet) into one library of programmatic
components available to developers to have significant productivity gains.
• Improve distributed computing interoperability by using open (non-
proprietary) standards that can enable (theoretically) any two software
components to communicate:
• Also they are easier to debug because they are text-based, rather than binary,
communication protocols
6

Web Services (contd…)
• Provide capabilities similar to those of EDI (Electronic Data Interchange), but are
simpler and less expensive to implement.
• Configured to work with EDI systems, allowing organisations to use the two
technologies together or to phase out EDI while adopting Web services.
• Unlike WWW
• Separates visual from non-visual components
• Interactions may be either through the browser or through a desktop client
(Java Swing, Python, Windows, etc.)
7

Web Services (contd…)
 Intended to solve three problems:
 Interoperability:
 Lack of interoperability standards in distributed object messaging
 DCOM apps strictly bound to Windows Operating system
 RMI bound to Java programming language
 Firewall traversal:
 CORBA and DCOM used non-standard ports
 Web Services use HTTP; most firewalls allow access though port 80 (HTTP), leading to easier and
dynamic collaboration
 Complexity:
 Web Services: developer-friendly service system
 Use open, text-based standards, which allow components written in different languages and for
different platforms to communicate
 Implemented incrementally, rather than all at once which lessens the cost and reduces the
organisational disruption from an abrupt switch in technologies
8

Web Service: Definition Revisited
• An application component that:
• Communicates via open protocols (HTTP, SMTP, etc.)
• Processes XML messages framed using SOAP
• Describes its messages using XML Schema
• Provides an endpoint description using WSDL
• Can be discovered using UDDI
9

Example: Web based purchase
Purchase
Order
Invoice
Consolidate
Results
PO Service
Credit Service
Inventory Service
FigureTaken from Oracle Session id: 40024

Service Oriented Architecture (SOA)
• IBM has created a model to show Web services interactions which is
referred to as a Service-Oriented Architecture (SOA) consisting of
relationships between three entities:
• A service provider;
• A service requestor;
• A service broker
• IBM’s SOA is a generic model describing service collaboration, not just
specific to Web services.
• See: http://www-106.ibm.com/developerworks/webservices/
11

Web Service Model (contd…)
• Roles in Web Service architecture
• Service provider
• Owner of the service
• Platform that hosts access to the service
• Service requestor
• Business that requires certain functions to be satisfied
• Application looking for and invoking an interaction with a service
• Service registry
• Searchable registry of service descriptions where service providers publish their service
descriptions
13

Web Service Model (contd…)
• Operations in a Web Service Architecture
• Publish
• Service descriptions need to be published in order for service requestor to find
them
• Find
• Service requestor retrieves a service description directly or queries the service
registry for the service required
• Bind
• Service requestor invokes or initiates an interaction with the service at runtime
14

Web Service Components
• XML – eXtensible Markup Language
• A uniform data representation and exchange mechanism.
• SOAP – Simple Object Access Protocol
• A standard way for communication.
• WSDL – Web Services Description Language
• A standard meta language to described the services offered.
• UDDI – Universal Description, Discovery and Integration specification
• A mechanism to register and locate WS based application.
15

Steps of Operation
1. Client queries registry to locate
service.
2. Registry refers client to WSDL
document.
3. Client accesses WSDL document.
4. WSDL provides data to interact with
Web service.
5. Client sends SOAP-message
request.
6. Web service returns SOAP-message
response.
WSDL
Docum
ent
UDDI
Registry
Web
Services
Client
1
2
3
4
5
6
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XML
• Developed from Standard Generalized Markup Method (SGML)
• Widely supported by W3C
• Essential characteristic is the separation of content from presentation
• Designed to describe data
• XML document can optionally reference a Document Type Definition (DTD),
also called a Schema
• XML parser checks syntax
• If an XML document adheres to the structure of the schema it is valid
18

XML (contd…)
• XML tags are not predefined
• You must define your own tags.
• Enables cross-platform data communication
in Web Services
19

XML vs HTML
An HTML example: <html>
<body>
<h2>John Doe</h2>
<p>2 Backroads Lane<br>
New York<br>
045935435<br>
john.doe@gmail.com<br>
</p>
</body>
</html>
20

XML vs HTML (contd…)
• This will be displayed as:
• HTML specifies how the document is to be displayed, and not what information is contained in
the document.
• Hard for machine to extract the embedded information. Relatively easy for human.
John Doe
2 Backroads Lane
New York
045935435
John.doe@gmail.com
21

XML vs HTML (contd…)
• Now look at the following:
• In this case:
• The information contained is being marked, but not for displaying.
• Readable by both human and machines.
<?xml version=1.0?>
<contact>
<name>John Doe</name>
<address>2 Backroads Lane</address>
<country>New York</country>
<phone>045935435</phone>
<email>john.doe@gmail.com</email>
</contact>
22

SOAP
• Simple Object Access Protocol
• Format for sending messages over Internet between programs
• XML-based
• Platform and language independent
• Simple and extensible
• Uses mainly HTTP as a transport protocol
• HTTP message contains a SOAP message as its payload section
• Stateless, one-way
• But applications can create more complex interaction patterns
23

SOAP Building Blocks
• Envelope (required) – identifies XML
document as SOAP message
• Header (optional) – contains header
information
• Body (required) –call and response
information
• Fault (optional) – errors that occurred
while processing message
SOAP BODY
SOAP ENVELOPE
FAULT
SOAP HEADER
Transport protocol
MIME header
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SOAP Message Structure
• Request and Response messages
• Request invokes a method on a remote object
• Response returns result of running the method
• SOAP specification defines an “envelop”
• “envelop” wraps the message itself
• Message is a different vocabulary
• Namespace prefix is used to distinguish the two
parts
Application-specific
message vocabulary
SOAP Envelop vocabulary
25

SOAP Request
POST /InStock HTTP/1.1
Host: www.stock.org
Content-Type: application/soap+xml; charset=utf-8 Content-Length: 150
<?xml version="1.0"?>
<soap:Envelope
xmlns:soap="http://www.w3.org/2001/12/soap-envelope"
soap:encodingStyle=http://www.w3.org/2001/12/soap-encoding”>
<soap:Body xmlns:m="http://www.stock.org/stock">
<m:GetStockPrice>
<m:StockName>IBM</m:StockName>
</m:GetStockPrice>
</soap:Body>
</soap:Envelope>
26

SOAP Response
HTTP/1.1 200 OK
Content-Type: application/soap; charset=utf-8
Content-Length: 126
<?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope"
soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">
<soap:Body xmlns:m="http://www.stock.org/stock">
<m:GetStockPriceResponse>
<m:Price>34.5</m:Price>
</m:GetStockPriceResponse>
</soap:Body>
</soap:Envelope>
27

Why SOAP?
• Other distributed technologies failed on the Internet
• Unix RPC – requires binary-compatible Unix implementations at each endpoint
• CORBA – requires compatible ORBs
• RMI – requires Java at each endpoint
• DCOM – requires Windows at each endpoint
• SOAP is the platform-neutral choice
• Simply an XML wire format
• Places no restrictions on the endpoint implementation technology choices
28

SOAP Characteristics
• SOAP has three major characteristics:
• Extensibility – security and WS-routing are among the extensions
under development.
• Neutrality - SOAP can be used over any transport protocol such as
HTTP, SMTP or even TCP.
• Independent - SOAP allows for any programming model.
29

SOAP Usage Models
• RPC-like message exchange
• Request message bundles up method name and parameters
• Response message contains method return values
• However, it isn’t required by SOAP
• SOAP specification allows any kind of body content
• Can be XML documents of any type
• Example:
• Send a purchase order document to the inbox of B2B partner
• Expect to receive shipping and exceptions report as response
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SOAP Security
• SOAP uses HTTP as a transport protocol and hence can use
HTTP security mainly HTTP over SSL.
• But, since SOAP can run over a number of application
protocols (such as SMTP) security had to be considered.
• The WS-Security specification defines a complete encryption
system.
31

WSDL - Web Service Definition Language
• WSDL : XML vocabulary standard for describing Web services and their
capabilities
• Contract between the XML Web service and the client
• Specifies what a request message must contain and what the response
message will look like in unambiguous notation
• Defines where the service is available and what communications
protocol is used to talk to the service.
32

WSDL Document Structure
• A WSDL document is just a simple XML document.
• It defines a web service using these major elements:
• port type - The operations performed by the web service.
• message - The messages used by the web service.
• types - The data types used by the web service.
• binding - The communication protocols used by the web service.
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<message name="getTermRequest">
<part name="term" type="xs:string"/>
</message>
<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>
A Sample WSDL
34

<message name="getTermRequest">
<part name="term" type="xs:string"/>
</message>
<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>
<binding type="glossaryTerms" name="b1">
<soap:binding style="document"
transport="http://schemas.xmlsoap.org/soap/http" />
<operation>
<soap:operation
soapAction="http://example.com/getTerm"/>
<input>
<soap:body use="literal"/>
</input>
<output>
<soap:body use="literal"/>
</output>
</operation>
</binding>
Binding to SOAP
35

UDDI - Universal Description, Discovery, and Integration
• A framework to define XML-based registries
• Registries are repositories that contain documents that describe business data and
also provide search capabilities and programmatic access to remote applications
• Businesses can publish information about themselves and the services they offer
• Can be interrogated by SOAP messages and provides access to WSDL documents
describing web services in its directory
36

UDDI Roles and Operations
•Service Registry
•Provides support for publishing and locating
services
•Like telephone yellow pages
•Service Provider
•Provides e-business services
•Publishes these services through a registry
•Service requestor
•Finds required services via the Service Broker
•Binds to services via Service Provider
37

UDDI Benefits
• Making it possible to discover the right business from the millions
currently online
• Defining how to enable commerce once the preferred business is
discovered
• Reaching new customers and increasing access to current customers
• Expanding offerings and extending market reach
39

SOAP
WS-Security
WS-Policy WS-Trust WS-Privacy
WS-Secure
Conversation WS-Federation WS-Authorization
Web Services Security Architecture
40

CLOUD COMPUTING
ARCHITECTURE - Deployment Models
IIT KHARAGPUR

Deployment Models
• Public Cloud
• Private Cloud
• Hybrid Cloud
• Community Cloud
2

Public Cloud
 Cloud infrastructure is provisioned for open use by the general
public. It may be owned, managed, and operated by a business,
academic, or government organization, or some combination of
them. It exists on the premises of the cloud provider.
 Examples of Public Cloud:
 Google App Engine
 Microsoft Windows Azure
 IBM Smart Cloud
 Amazon EC2
Source:Marcus Hogue,Chris Jacobson,”Security of Cloud Computing”
3

Public Cloud
• In Public setting, the provider's computing and storage resources are
potentially large; the communication links can be assumed to be
implemented over the public Internet; and the cloud serves a diverse pool
of clients (and possibly attackers).
Source: LeeBadger, and Tim Grance “NIST DRAFT Cloud Computing Synopsis and Recommendations “
4

Public Cloud
• Workload locations are hidden from clients (public):
– In the public scenario, a provider may migrate a subscriber's workload,
whether processing or data, at any time.
– Workload can be transferred to data centres where cost is low
– Workloads in a public cloud may be relocated anywhere at any time
unless the provider has offered (optional) location restriction policies
• Risks from multi-tenancy (public):
– A single machine may be shared by the workloads of any combination
of subscribers (a subscriber's workload may be co-resident with the
workloads of competitors or adversaries)
• Introduces both reliability and security risk
5

Public Cloud
• Organizations considering the use of an on-site private cloud
should consider:
– Network dependency (public):
• Subscribers connect to providers via the public Internet.
• Connection depends on Internet’s Infrastructure like
– Domain Name System (DNS) servers
– Router infrastructure,
– Inter-router links
6

Public Cloud
• Limited visibility and control over data regarding security (public):
– The details of provider system operation are usually considered proprietary
information and are not divulged to subscribers.
– In many cases, the software employed by a provider is usually proprietary and not
available for examination by subscribers
– A subscriber cannot verify that data has been completely deleted from a
provider's systems.
• Elasticity: illusion of unlimited resource availability (public):
– Public clouds are generally unrestricted in their location or size.
– Public clouds potentially have high degree of flexibility in the movement of
subscriber workloads to correspond with available resources.
7

Public Cloud
• Low up-front costs to migrate into the cloud (public)
• Restrictive default service level agreements (public):
– The default service level agreements of public clouds specify
limited promises that providers make to subscribers
8

Private Cloud
• The cloud infrastructure is provisioned for exclusive use by a single organization
comprising multiple consumers (e.g., business units). It may be owned, managed,
and operated by the organization, a third party, or some combination of them, and
it may exist on or off premises.
• Examples of Private Cloud:
– Eucalyptus
– Ubuntu Enterprise Cloud - UEC
– Amazon VPC (Virtual Private Cloud)
– VMware Cloud Infrastructure Suite
– Microsoft ECI data center.
9

Private Cloud
• Contrary to popular belief, private cloud may exist off premises and
can be managed by a third party. Thus, two private cloud scenarios
exist, as follows:
• On-site Private Cloud
– Applies to private clouds implemented at a customer’s
premises.
• Outsourced Private Cloud
– Applies to private clouds where the server side is outsourced to
a hosting company.
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On-site Private Cloud
 The security perimeter extends around both the subscriber’s on-site
resources and the private cloud’s resources.
 Security perimeter does not guarantees control over the private cloud’s
resources but subscriber can exercise control over the resources.
11

• Organizations considering the use of an on-site private cloud should consider:
– Network dependency (on-site-private):
– Subscribers still need IT skills (on-site-private):
• Subscriber organizations will need the traditional IT skills required to
manage user devices that access the private cloud, and will require
cloud IT skills as well.
– Workload locations are hidden from clients (on-site-private):
• To manage a cloud's hardware resources, a private cloud must be able
to migrate workloads between machines without inconveniencing
clients. With an on-site private cloud, however, a subscriber
organization chooses the physical infrastructure, but individual clients
still may not know where their workloads physically exist within the
subscriber organization's infrastructure
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• Risks from multi-tenancy (on-site-private):
– Workloads of different clients may reside concurrently on the same
systems and local networks, separated only by access policies
implemented by a cloud provider's software. A flaw in the software or
the policies could compromise the security of a subscriber
organization by exposing client workloads to one another
• Data import/export, and performance limitations (on-site-private):
– On-demand bulk data import/export is limited by the on-site private
cloud's network capacity, and real-time or critical processing may be
problematic because of networking limitations.
13

• Potentially strong security from external threats (on-site-private):
– In an on-site private cloud, a subscriber has the option of implementing an
appropriately strong security perimeter to protect private cloud resources against
external threats to the same level of security as can be achieved for non-cloud
resources.
• Significant-to-high up-front costs to migrate into the cloud (on-site-private):
– An on-site private cloud requires that cloud management software be installed on
computer systems within a subscriber organization. If the cloud is intended to support
process-intensive or data-intensive workloads, the software will need to be installed on
numerous commodity systems or on a more limited number of high-performance
systems. Installing cloud software and managing the installations will incur significant
up-front costs, even if the cloud software itself is free, and even if much of the hardware
already exists within a subscriber organization.
14

• Limited resources (on-site-private):
– An on-site private cloud, at any specific time, has a fixed computing
and storage capacity that has been sized to correspond to anticipated
workloads and cost restrictions.
15

Outsourced Private Cloud
• Outsourced private cloud has two security perimeters, one implemented
by a cloud subscriber (on the right) and one implemented by a provider.
• Two security perimeters are joined by a protected communications link.
• The security of data and processing conducted in the outsourced private
cloud depends on the strength and availability of both security perimeters
and of the protected communication link.
16

• Organizations considering the use of an outsourced private cloud should
consider:
– Network Dependency (outsourced-private):
• In the outsourced private scenario, subscribers may have an option to
provision unique protected and reliable communication links with the
provider.
– Workload locations are hidden from clients (outsourced-private):
– Risks from multi-tenancy (outsourced-private):
• The implications are the same as those for an on-site private cloud.
17

• Data import/export, and performance limitations (outsourced-private):
– On-demand bulk data import/export is limited by the network capacity
between a provider and subscriber, and real-time or critical processing
may be problematic because of networking limitations. In the outsourced
private cloud scenario, however, these limits may be adjusted, although
not eliminated, by provisioning high-performance and/or high-reliability
networking between the provider and subscriber.
• Potentially strong security from external threats (outsourced-private):
– As with the on-site private cloud scenario, a variety of techniques exist to
harden a security perimeter. The main difference with the outsourced
private cloud is that the techniques need to be applied both to a
subscriber's perimeter and provider's perimeter, and that the
communications link needs to be protected.
18

• Modest-to-significant up-front costs to migrate into the cloud (outsourced-
private):
– In the outsourced private cloud scenario, the resources are provisioned by
the provider
– Main start-up costs for the subscriber relate to:
• Negotiating the terms of the service level agreement (SLA)
• Possibly upgrading the subscriber's network to connect to the
outsourced private cloud
• Switching from traditional applications to cloud-hosted applications,
• Porting existing non-cloud operations to the cloud
• Training
19

• Extensive resources available (outsourced-private):
– In the case of the outsourced private cloud, a subscriber can rent
resources in any quantity offered by the provider. Provisioning and
operating computing equipment at scale is a core competency of
providers.
20

Community Cloud
 Cloud infrastructure is provisioned for exclusive use by a specific community of
consumers from organizations that have shared concerns (e.g., mission, security
requirements, policy, and compliance considerations). It may be owned,
managed, and operated by one or more of the organizations in the community,
a third party, or some combination of them, and it may exist on or off premises.
 Examples of Community Cloud:
 Google Apps for Government
 Microsoft Government Community
Cloud
21

On-site Community Cloud
• Community cloud is made up of a set of participant organizations. Each participant
organization may provide cloud services, consume cloud services, or both
• At least one organization must provide cloud services
• Each organization implements a security perimeter
22

• The participant organizations are connected via links between the
boundary controllers that allow access through their security perimeters
• Access policy of a community cloud may be complex
– Ex. :if there are N community members, a decision must be made,
either implicitly or explicitly, on how to share a member's local cloud
resources with each of the other members
– Policy specification techniques like role-based access control (RBAC),
attribute-based access control can be used to express sharing policies.
23

• Organizations considering the use of an on-site community cloud should consider:
– Network Dependency (on-site community):
• The subscribers in an on-site community cloud need to either
provision controlled inter-site communication links or use
cryptography over a less controlled communications media (such
as the public Internet).
• The reliability and security of the community cloud depends on
the reliability and security of the communication links.
24

• Subscribers still need IT skills (on-site-community).
– Organizations in the community that provides cloud resources, requires IT
skills similar to those required for the on-site private cloud scenario except
that the overall cloud configuration may be more complex and hence
require a higher skill level.
– Identity and access control configurations among the participant
organizations may be complex
• Workload locations are hidden from clients (on-site-community):
– Participant Organizations providing cloud services to the community cloud
may wish to employ an outsourced private cloud as a part of its
implementation strategy.
25

• Data import/export, and performance limitations (on-site-community):
– The communication links between the various participant organizations in
a community cloud can be provisioned to various levels of performance,
security and reliability, based on the needs of the participant
organizations. The network-based limitations are thus similar to those of
the outsourced-private cloud scenario.
• Potentially strong security from external threats (on-site-community):
– The security of a community cloud from external threats depends on the
security of all the security perimeters of the participant organizations and
the strength of the communications links. These dependencies are
essentially similar to those of the outsourced private cloud scenario, but
with possibly more links and security perimeters.
26

• Highly variable up-front costs to migrate into the cloud (on-site-
community):
– The up-front costs of an on-site community cloud for a participant
organization depend greatly on whether the organization plans to
consume cloud services only or also to provide cloud services. For
a participant organization that intends to provide cloud services
within the community cloud, the costs appear to be similar to
those for the on-site private cloud scenario (i.e., significant-to-
high).
27

Outsourced Community Cloud
28

• Organizations considering the use of an on-site community cloud
should consider:
• Network dependency (outsourced-community):
– The network dependency of the outsourced community cloud is
similar to that of the outsourced private cloud. The primary
difference is that multiple protected communications links are
likely from the community members to the provider's facility.
• Workload locations are hidden from clients (outsourced-
community).
– Same as the outsourced private cloud
29

• Risks from multi-tenancy (outsourced-community):
– Same as the on-site community cloud
• Data import/export, and performance limitations (outsourced-
community):
– Same as outsourced private cloud
• Potentially strong security from external threats (outsourced-
community):
– Same as the on-site community cloud
• Modest-to-significant up-front costs to migrate into the cloud
(outsourced-community):
• Same as outsourced private cloud
30

• Extensive resources available (outsourced-community).
– Same as outsourced private cloud
31

Hybrid Cloud
• The cloud infrastructure is a composition of two or more distinct cloud
infrastructures (private, community, or public) that remain unique entities,
but are bound together by standardized or proprietary technology that
enables data and application portability
• Examples of Hybrid Cloud:
– Windows Azure (capable of Hybrid Cloud)
– VMware vCloud (Hybrid Cloud Services)
32

Hybrid Cloud
• A hybrid cloud is composed of two or more private, community, or public
clouds.
• They have significant variations in performance, reliability, and security
properties depending upon the type of cloud chosen to build hybrid cloud.
33

Hybrid Cloud
• A hybrid cloud can be extremely complex
• A hybrid cloud may change over time with constituent clouds
joining and leaving.
34

CLOUD COMPUTING
Virtualization
IIT KHARAGPUR

IaaS – Infrastructure as a Service
• What does a subscriber get?
– Access to virtual computers, network-accessible storage, network
infrastructure components such as firewalls, and configuration services.
• How are usage fees calculated?
– Typically, per CPU hour, data GB stored per hour, network bandwidth
consumed, network infrastructure used (e.g., IP addresses) per hour,
value-added services used (e.g., monitoring, automatic scaling)
2

IaaS Provider/Subscriber Interaction Dynamics
• The provider has a number of available virtual machines
(vm’s) that it can allocate to clients.
– Client A has access to vm1 and vm2, Client B has access to vm3 and Client C has
access to vm4, vm5 and vm6
– Provider retains only vm7 through vmN
3

IaaS Component Stack and Scope of Control
• IaaS component stack comprises of hardware, operating system,
middleware, and applications layers.
• Operating system layer is split into two layers.
– Lower (and more privileged) layer is occupied by the Virtual Machine Monitor (VMM),
which is also called the Hypervisor
– Higher layer is occupied by an operating system running within a VM called a guest
operating system
4

• In IaaS Cloud provider maintains total control over the
physical hardware and administrative control over the
hypervisor layer
• Subscriber controls the Guest OS, Middleware and
Applications layers.
• Subscriber is free (using the provider's utilities) to load any
supported operating system software desired into the VM.
• Subscriber typically maintains complete control over the
operation of the guest operating system in each VM.
5

• A hypervisor uses the hardware to synthesize one or more
Virtual Machines (VMs); each VM is "an efficient, isolated
duplicate of a real machine" .
• Subscriber rents access to a VM, the VM appears to the
subscriber as actual computer hardware that can be
administered (e.g., powered on/off, peripherals configured) via
commands sent over a network to the provider.
6

IaaS Cloud Architecture
• Logical view of IaaS cloud structure and operation
7

• Three-level hierarchy of components in IaaS cloud systems
– Top level is responsible for central control
– Middle level is responsible for management of possibly large
computer clusters that may be geographically distant from one
another
– Bottom level is responsible for running the host computer systems on
which virtual machines are created.
• Subscriber queries and commands generally flow into the system
at the top and are forwarded down through the layers that either
answer the queries or execute the commands
8

• Cluster Manager can be geographically
distributed
• Within a cluster manger computer manger is
connected via high speed network.
9

Operation of the Cloud Manager
• Cloud Manager is the public access point to the cloud where
subscribers sign up for accounts, manage the resources they rent
from the cloud, and access data stored in the cloud.
• Cloud Manager has mechanism for:
– Authenticating subscribers
– Generating or validating access credentials that subscriber uses when
communicating with VMs.
– Top-level resource management.
• For a subscriber’s request cloud manager determines if the cloud
has enough free resources to satisfy the request
10

Data Object Storage (DOS)
• DOS generally stores the subscriber’s metadata like user credentials,
operating system images.
• DOS service is (usually) single for a cloud.
11

Operation of the Cluster Managers
• Each Cluster Manager is responsible for the operation of a collection of
computers that are connected via high speed local area networks
• Cluster Manager receives resource allocation commands and queries
from the Cloud Manager, and calculates whether part or all of a
command can be satisfied using the resources of the computers in the
cluster.
• Cluster Manager queries the Computer Managers for the computers in
the cluster to determine resource availability, and returns messages to
the Cloud Manager
12

Operation of the Cluster Managers
• Directed by the Cloud Manager, a Cluster Manager then
instructs the Computer Managers to perform resource
allocation, and reconfigures the virtual network infrastructure
to give the subscriber uniform access.
• Each Cluster Manager is connected to Persistent Local Storage
(PLS)
• PLS provide persistent disk-like storage to Virtual Machine
13

Operation of the Computer Managers
• At the lowest level in the hierarchy computer manger runs on each
computer system and uses the concept of virtualization to provide Virtual
Machines to subscribers
• Computer Manger maintains status information including how many
virtual machines are running and how many can still be started
• Computer Manager uses the command interface of its hypervisor to start,
stop, suspend, and reconfigure virtual machines
14

Virtualization
Operating System
App. A App. B App. C App. D
Hardware
Virtualization Layer
Virtual
Container
App. A App. B
Hardware
Virtual
Container
App. C App. D
‘Non-virtualized’ system
A single OS controls all hardware platform
resources
Virtualized system
It makes it possible to run multiple Virtual
Containers on a single physical platform
• Virtualization is a broad term (virtual memory, storage, network, etc)
• Focus: Platform virtualization
• Virtualization basically allows one computer to do the job of multiple computers, by sharing the
resources of a single hardware across multiple environments
Source: www.dc.uba.ar/events/eci/2008/courses/n2/Virtualization-Introduction.ppt
15

Virtualization• Virtualization is way to run multiple operating systems and user applications on the
same hardware
– E.g., run both Windows and Linux on the same laptop
• How is it different from dual-boot?
– Both OSes run simultaneously
• The OSes are completely isolated from each other
16

Hypervisor or Virtual Machine Monitor
Research Paper :Popek and Goldberg, "Formal requirements for virtualizable third generation architectures“, CACM 1974
(http://portal.acm.org/citation.cfm?doid=361011.361073).
A hypervisor or virtual machine monitor runs the guest OS directly on the CPU. (This only works if
the guest OS uses the same instruction set as the host OS.) Since the guest OS is running in user
mode, privileged instructions must be intercepted or replaced. This further imposes restrictions on
the instruction set for the CPU, as observed in a now-famous paper by Popek and Goldberg
identify three goals for a virtual machine architecture:
• Equivalence: The VM should be indistinguishable from the underlying hardware.
• Resource control: The VM should be in complete control of any virtualized resources.
• Efficiency: Most VM instructions should be executed directly on the underlying CPU without
involving the hypervisor.
17

Hypervisor or Virtual Machine Monitor
Popek and Goldberg describe (and give a formal proof of) the requirements for the CPU's
instruction set to allow these properties. The main idea here is to classify instructions into
• privileged instructions, which cause a trap if executed in user mode, and
• sensitive instructions, which change the underlying resources (e.g. doing I/O or changing the
page tables) or observe information that indicates the current privilege level (thus exposing
the fact that the guest OS is not running on the bare hardware).
• The former class of sensitive instructions are called control sensitive and the latter behavior
sensitive in the paper, but the distinction is not particularly important.
What Popek and Goldberg show is that we can only run a virtual machine with all three desired
properties if the sensitive instructions are a subset of the privileged instructions. If this is the case,
then we can run most instructions directly, and any sensitive instructions trap to the hypervisor
which can then emulate them (hopefully without much slowdown).
18

VMM and VM
Equivalence
Resource Control
Efficiency
Privileged instructions
Control sensitive
Behavior sensitive
• For any conventional third generation computer, a VMM may be constructed if the set of sensitive
instructions for that computer is a subset of the set of privileged instructions
• A conventional third generation computer is recursively virtualizable if it is virtualizable and a VMM without
any timing dependencies can be constructed for it.
19

Approaches to Server Virtualization
20

Evolution of Software Solutions
• 1st Generation: Full
virtualization (Binary
rewriting)
– Software Based
– VMware and
Microsoft
Time
• 3rd Generation: Silicon-
based (Hardware-
assisted) virtualization
– Unmodified guest
– VMware and Xen on
virtualization-aware
hardware platforms
• 2nd Generation:
Para-virtualization
– Cooperative
virtualization
– Modified guest
– VMware, Xen
Dynamic Translation
Virtual
Machine
Hardware
Operating System
Virtual
Machine…
Hypervisor
Hardware
VMVM
Hardware
Virtual
Machine
Virtual
Machine…
Virtualization Logic
Hypervisor
…
21

Full Virtualization
• 1st Generation offering of x86/x64 server
virtualization
• Dynamic binary translation
– Emulation layer talks to an operating system which
talks to the computer hardware
– Guest OS doesn't see that it is used in an emulated
environment
• All of the hardware is emulated including the CPU
• Two popular open source emulators are QEMU
and Bochs
Emulated
Hardware
VirtualMachine
GuestOS
Device Drivers
App.A
App.B
App.C
Hardware
Host OS
Device Drivers
22

Full Virtualization - Advantages
• Emulation layer
– Isolates VMs from the host OS and from each other
– Controls individual VM access to system resources, preventing an unstable VM
from impacting system performance
• Total VM portability
– By emulating a consistent set of system hardware, VMs have the ability to
transparently move between hosts with dissimilar hardware without any
problems
• It is possible to run an operating system that was developed for another
architecture on your own architecture
• A VM running on a Dell server can be relocated to a Hewlett-Packard server
23

Full Virtualization - Drawbacks
• Hardware emulation comes with a performance price
• In traditional x86 architectures, OS kernels expect to run privileged code in
Ring 0
– However, because Ring 0 is controlled by the host OS, VMs are forced to execute
at Ring 1/3, which requires the VMM to trap and emulate instructions
• Due to these performance limitations, para-virtualization and hardware-
assisted virtualization were developed
Application Ring 3
Operating
System
Ring 0
Traditional x86 Architecture
Application Ring 3
Guest OS Ring 1 / 3
Virtual
Machine
Monitor
Ring 0
Full Virtualization
24

Para-Virtualization
• Guest OS is modified and thus run kernel-level
operations at Ring 1 (or 3)
– Guest is fully aware of how to process privileged
instructions
– Privileged instruction translation by the VMM is no
longer necessary
– Guest operating system uses a specialized API to talk to
the VMM and, in this way, execute the privileged
instructions
• VMM is responsible for handling the virtualization
requests and putting them to the hardware
Virtual Machine Monitor
VirtualMachine
GuestOS
Device Drivers
App.A
App.B
App.C
Specialized API
Hardware
Hypervisor
Device Drivers
Server virtualization approaches
25

Para-Virtualization
• Today, VM guest operating systems are para-virtualized using two different approaches:
– Recompiling the OS kernel
• Para-virtualization drivers and APIs must reside in the guest operating system kernel
• You do need a modified operating system that includes this specific API, requiring a compiling operating
systems to be virtualization aware
– Some vendors (such as Novell) have embraced para-virtualization and have provided para-virtualized
OS builds, while other vendors (such as Microsoft) have not
– Installing para-virtualized drivers
• In some operating systems it is not possible to use complete para-virtualization, as it requires a specialized
version of the operating system
• To ensure good performance in such environments, para-virtualization can be applied for individual devices
• For example, the instructions generated by network boards or graphical interface cards can be modified
before they leave the virtualized machine by using para-virtualized drivers
26

Hardware-assisted virtualization
• Guest OS runs at ring 0
• VMM uses processor extensions (such as Intel®-
VT or AMD-V) to intercept and emulate
privileged operations in the guest
• Hardware-assisted virtualization removes many
of the problems that make writing a VMM a
challenge
• VMM runs in a more privileged ring than 0, a
Virtual-1 ring is created
Virtual Machine Monitor
VirtualMachine
GuestOS
Device Drivers
App.A
App.B
App.C
Specialized API
Hardware
Hypervisor
Device Drivers
27

Hardware-assisted virtualization
• Pros
– It allows to run unmodified OSs (so legacy OS can be run without
problems)
• Cons
– Speed and Flexibility
• An unmodified OS does not know it is running in a virtualized
environment and so, it can’t take advantage of any of the
virtualization features
– It can be resolved using para-virtualization partially
28

Network Virtualization
29
Making a physical network appear as multiple logical ones
Physical Network Virtualized Network - 1 Virtualized Network - 2

Why Virtualize ?
30
• Internet is almost “paralyzed”
– Lots of makeshift solutions (e.g. overlays)
– A new architecture (aka clean-slate) is needed
• Hard to come up with a one-size-fits-all architecture
– Almost impossible to predict what future might unleash
• Why not create an all-sizes-fit-into-one instead!
– Open and expandable architecture
• Testbed for future networking architectures and protocols

Related Concepts
31
• Virtual Private Networks (VPN)
– Virtual network connecting distributed sites
– Not customizable enough
• Active and Programmable Networks
– Customized network functionalities
– Programmable interfaces and active codes
• Overlay Networks
– Application layer virtual networks
– Not flexible enough

Network Virtualization Model
32
• Business Model
• Architecture
• Design Principles
• Design Goals

Business Model
• Infrastructure Providers (InPs)
– Manage underlying physical networks
• Service Providers (SPs)
– Create and manage virtual networks
– Deploy customized end-to-end services
• End Users
– Buy and use services from different service
providers
• Brokers
– Mediators/Arbiters
33
Players Relationships
End User
Service Provider
Infrastructure
Provider
Broker
IIA
SIA
NPA
SLA
EIA

Design Principles
 Concurrence of multiple
heterogeneous virtual networks
 Introduces diversity
 Recursion of virtual networks
 Opens the door for network virtualization
economics
 Inheritance of architectural attributes
 Promotes value-addition
 Revisitation of virtual nodes
 Simplifies network operation and
management
35
Hierarchy of Roles
Service Provider 0
Infrastructure
Provider 0
Infrastructure
Provider 1
Virtual Network 0
Service Provider 1
Infrastructure
Provider 2
Virtual Network 1
Service Provider N
Infrastructure
Provider N+1
Virtual Network N
…

Design Goals (1)
36
• Flexibility
– Service providers can choose
• arbitrary network topology,
• routing and forwarding functionalities,
• customized control and data planes
– No need for co-ordination with others
• IPv6 fiasco should never happen again
• Manageability
– Clear separation of policy from mechanism
– Defined accountability of infrastructure and service providers
– Modular management

Design Goals (2)
37
• Scalability
– Maximize the number of co-existing virtual networks
– Increase resource utilization and amortize CAPEX and OPEX
• Security, Privacy, and Isolation
– Complete isolation between virtual networks
• Logical and resource
– Isolate faults, bugs, and misconfigurations
• Secured and private

Design Goals (3)
38
• Programmability
– Of network elements e.g. routers
– Answer “How much” and “how”
– Easy and effective without being vulnerable to threats
• Heterogeneity
– Networking technologies
• Optical, sensor, wireless etc.
– Virtual networks

Design Goals (4)
39
• Experimental and Deployment Facility
– PlanetLab, GENI, VINI
– Directly deploy services in real world from the testing phase
• Legacy Support
– Consider the existing Internet as a member of the collection of
multiple virtual Internets
– Very important to keep all concerned parties satisfied

Definition
40
Network virtualization is a networking environment that allows
multiple service providers to dynamically compose multiple
heterogeneous virtual networks that co-exist together in
isolation from each other, and to deploy customized end-to-
end services on-the-fly as well as manage them on those
virtual networks for the end-users by effectively sharing and
utilizing underlying network resources leased from multiple
infrastructure providers.

Typical Approach
41
• Networking technology
– IP, ATM
• Layer of virtualization
• Architectural domain
– Network resource management, Spawning networks
• Level of virtualization
– Node virtualization, Full virtualization

1
Introduction to XML:
eXtensible Markup Language
Prof. Soumya K Ghosh
Department of Computer Science and Engineering
IIT KHARAGPUR

2
XML ??
• Over time, the acronym “XML” has evolved to imply a growing family of
software tools/XML standards/ideas around
– How XML data can be represented and processed
– application frameworks (tools, dialects) based on XML
• Most “popular” XML discussion refers to this latter meaning
• We’ll talk about both.

3
Presentation Outline
• What is XML (basic introduction)
– Language rules, basic XML processing
• Defining language dialects
– DTDs, schemas, and namespaces
• XML processing
– Parsers and parser interfaces
– XML-based processing tools
• XML messaging
– Why, and some issues/example
• Conclusions

4
• A syntax for “encoding” text-based data (words, phrases, numbers, ...)
• A text-based syntax. XML is written using printable Unicode characters (no explicit
binary data; character encoding issues)
• Extensible. XML lets you define your own elements (essentially data types), within
the constraints of the syntax rules
• Universal format. The syntax rules ensure that all XML processing software MUST
identically handle a given piece of XML data.
What is XML?
If you can read and process it, so can
anybody else

5
What is XML: A Simple Example
XML Declaration (“this is XML”) Binary encoding used in file
<?xml version="1.0" encoding="iso-8859-1"?>
<partorders
xmlns=“http://myco.org/Spec/partorders”>
<order ref=“x23-2112-2342”
date=“25aug1999-12:34:23h”>
<desc> Gold sprockel grommets,
with matching hamster
</desc>
<part number=“23-23221-a12” />
<quantity units=“gross”> 12 </quantity>
<deliveryDate date=“27aug1999-12:00h” />
</order>
<order ref=“x23-2112-2342”
date=“25aug1999-12:34:23h”>
. . . Order something else . . .
</order>
</partorders>

6
Example Revisited
<partorders
xmlns=“http://myco.org/Spec/partorders” >
<order ref=“x23-2112-2342”
date=“25aug1999-12:34:23h”>
<desc> Gold sprockel grommets,
with matching hamster
</desc>
<part number=“23-23221-a12” />
<quantity units=“gross”> 12 </quantity>
<deliveryDate date=“27aug1999-12:00h” />
</order>
<order ref=“x23-2112-2342”
date=“25aug1999-12:34:23h”>
. . . Order something else . . .
</order>
</partorders> Hierarchical, structured information
tags attribute of this
quantity element
element

7
XML Data Model - A Tree
text
partorders
order
order
desc
part
quantity
delivery-date
date=
ref=
date=
ref=
xmlns=
<partorders xmlns="...">
<order date="..."
ref="...">
<desc> ..text..
</desc>
<part />
<quantity />
<delivery-date />
</order>
<order ref=".." .../>
</partorders>
text

8
XML: Why it's this way
• Simple (like HTML -- but not quite so simple)
– Strict syntax rules, to eliminate syntax errors
– syntax defines structure (hierarchically), and names structural parts (element names) -- it is self-describing
data
• Extensible (unlike HTML; vocabulary is not fixed)
– Can create your own language of tags/elements
– Strict syntax ensures that such markup can be reliably processed
• Designed for a distributed environment (like HTML)
– Can have data all over the place: can retrieve and use it reliably
• Can mix different data types together (unlike HTML)
– Can mix one set of tags with another set: resulting data can still be reliably processed

9
XML Processing<?xml version="1.0" encoding="utf-8" ?>
<transfers>
<fundsTransfer date="20010923T12:34:34Z">
<from type="intrabank">
<amount currency="USD"> 1332.32 </amount>
<transitID> 3211 </transitID>
<accountID> 4321332 </accountID>
<acknowledgeReceipt> yes </acknowledgeReceipt>
</from>
<to account="132212412321" />
</fundsTransfer>
<from type="internal">
<amount currency="CDN" >1432.12 </amount>
<accountID> 543211 </accountID>
<acknowledgeReceipt> yes </acknowledgeReceipt>
</from>
<to account="65123222" />
</fundsTransfer>
</transfers>
xml-simple.xml

10
XML Parser Processing Model
XML data
parser
parser
interface
XML-based
application
 The parser must verify that the XML data is syntactically correct.
 Such data is said to be well-formed
– The minimal requirement to “be” XML
 A parser MUST stop processing if the data isn’t well-formed
– E.g., stop processing and “throw an exception” to the XML-based application.
The XML 1.0 spec requires this behaviour

11
XML Processing Rules: Including Parts
<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE transfers [

<!ENTITY messageHeader
"<header>
<routeID> info generic to message route </routeID>
<encoding>how message is encoded </encoding>
</header> "
>
]>
<transfers>
&messageHeader;
. . . Content omitted . . .
</transfers> xml-simple-intEntity.xml
Document Type
Declaration (DTD)
Internal Entity
declaration
Entity reference
&name;

12
XML data
parser
parser
interface
XML-based
application
DTD

13
XML Parsers, DTDs, and Internal Entities
 The parser processes the DTD content, identifies the internal entities, and checks
that each entity is well-formed.
 There are explicit syntax rules for DTD content -- well-formed XML must be correct
here also.
 The parser then replaces every occurrence of an entity reference by the
referenced entity (and does so recursively within entities)
 The “resolved” data object is then made available to the XML application

14
XML Processing Rules: External Entities
<?xml version="1.0" encoding="utf-8" ?>
. . .
<!ENTITY messageHeader
SYSTEM "http://www.somewhere.org/dir/head.xml"
>
]>
<transfers>
&messageHeader;
. . . Content omitted . . .
</transfers> xml-simple-extEntity.xml
External Entity
declaration
Location given
via a URL
Put the entity in another file -- so it can be shared by multiple resources.

15
XML Parsers and External Entities
 The parser processes the DTD content, identifies the external entities, and “tries” to
resolve them
 The parser then replaces every occurrence of an entity reference by the
referenced entity, and does so recursively within all those entities, (like with internal
entities)
 But …. what if the parser can’t find the external entity (firewall?)?
 That depends on the application / parser type
– There are two types of XML parsers
– one that MUST retrieve all entities, and one that can ignore them (if it can’t find them)

16
Two types of XML parsers
 Validating parser
– Must retrieve all entities and must process all DTD content. Will stop processing and
indicate a failure if it cannot
– There is also the implication that it will test for compatibility with other things in the DTD --
instructions that define syntactic rules for the document (allowed elements, attributes,
etc.). We’ll talk about these parts in the next section.
 Non-validating parser
– Will try to retrieve all entities defined in the DTD, but will cease processing the DTD
content at the first entity it can’t find, But this is not an error -- the parser simply makes
available the XML data (and the names of any unresolved entities) to the
application.
Application behavior will depend on parser type

17
XML data
parser
parser
interface
XML-based
application
DTD
Relationship/
behavior
depends on
parser nature Many parsers can operate in
either
validating or non-validating mode
(parameter-dependent)

18
Special Issues: Characters and Charsets
• XML specification defines what characters can be used as whitespace in tags: <element id
= “23.112” />
• You cannot use EBCIDIC character ‘NEL’ as whitespace
– Must make sure to not do so!
• What if you want to include characters not defined in the encoding charset (e.g., Greek characters
in an ISO-Latin-1 document):
• Use character references. For example:
♠ -- the spades character ()
9824th character in the Unicode character set
• Also, binary data must be encoded as printable characters

19
• XML processing
• XML messaging
• Conclusions

20
How do you define language dialects?
• Two ways of doing so:
– XML Document Type Declaration (DTD) -- Part of core XML spec.
– XML Schema -- New XML specification (2001), which allows for stronger constraints on XML documents.
• Adding dialect specifications implies two classes of XML data:
– Well-formed An XML document that is syntactically correct
– Valid An XML document that is both well-formed and
consistent with a specific DTD (or Schema)
• What DTDs and/or schema specify:
– Allowed element and attribute names, hierarchical nesting rules; element content/type restrictions
• Schemas are more powerful than DTDs. They are often used for type validation, or for relating
database schemas to XML models

21
Example DTD (as part of document)
<!ELEMENT transfers (fundsTransfer)+ >
<!ELEMENT fundsTransfer (from, to) >
<!ATTLIST fundsTransfer
date CDATA #REQUIRED>
<!ELEMENT from (amount, transitID?, accountID,
acknowledgeReceipt ) >
<!ATTLIST from
type (intrabank|internal|other) #REQUIRED>
<!ELEMENT amount (#PCDATA) >
. . . Omitted DTD content . . .
<!ELEMENT to EMPTY >
<!ATTLIST to
account CDATA #REQUIRED>
]>
<transfers>
. . . As with previous example . . .
xml-simple-valid.xml

22
Example “External” DTD
<!DOCTYPE transfers SYSTEM
"http://www.foo.org/hereitis/simple.dtd” >
<transfers>
. . . As with previous example . . .
. . .
</transfers>
 Reference is using a variation on the DOCTYPE:
 Of course, the DTD file must be there, and accessible.
simple.dtd

2
XML Schemas
• A new specification (2001) for specifying validation rules for XML
Specs: http://www.w3.org/XML/Schema
Best-practice: http://www.xfront.com/BestPracticesHomepage.html
• Uses pure XML (no special DTD grammar) to do this.
• Schemas are more powerful than DTDs - can specify things like integer types, date
strings, real numbers in a given range, etc.
• They are often used for type validation, or for relating database schemas to XML
models
• They don’t, however, let you declare entities -- those can only be done in DTDs.
• The following slide shows the XML schema equivalent to our DTD

3
XML Schema version of our DTD (Portion)
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified">
<xs:element name="accountID" type="xs:string"/>
<xs:element name="acknowledgeReceipt" type="xs:string"/>
<xs:complexType name="amountType">
<xs:simpleContent>
<xs:restriction base="xs:string">
<xs:attribute name="currency" use="required">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="USD"/>
. . . (some stuff omitted) . . .
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:restriction>
</xs:simpleContent>
</xs:complexType>
<xs:complexType name="fromType">
<xs:sequence>
<xs:element name="amount" type="amountType"/>
<xs:element ref="transitID" minOccurs="0"/>
<xs:element ref="accountID"/>
<xs:element ref="acknowledgeReceipt"/>
</xs:sequence>
. . .
simple.xsd

4
XML Namespaces
• Mechanism for identifying different “spaces” for XML names
– That is, element or attribute names
• This is a way of identifying different language dialects, consisting of names that have specific
semantic (and processing) meanings.
• Thus <key/> in one language (might mean a security key) can be distinguished from <key/> in
another language (a database key)
• Mechanism uses a special xmlns attribute to define the namespace. The namespace is given as
a URL string
– But the URL does not reference anything in particular (there may be nothing there)

5
Mixing language dialects together
<?xml version= "1.0" encoding= "utf-8" ?>
<html xmlns="http://www.w3.org/1999/xhtml1"
xmlns:mt="http://www.w3.org/1998/mathml” >
<head>
<title> Title of XHTML Document </title>
</head><body>
<div class="myDiv">
<h1> Heading of Page </h1>
<mt:mathml>
<mt:title> ... MathML markup . . .
</mt:mathml>
<p> more html stuff goes here </p>
</div>
</body>
</html>
mt: prefix indicates ‘space’
mathml (a different language)
Default „space‟
is xhtml
Namespaces let you do this relatively easily:

6
 What is XML (basic introduction)
 Defining language dialects
 XML processing
 XML messaging
 Conclusions

7
XML Software
• XML parser -- Reads in XML data, checks for syntactic (and possibly DTD/Schema) constraints,
and makes data available to an application. There are three 'generic' parser APIs
– SAX Simple API to XML (event-based)
– DOM Document Object Model (object/tree based)
– JDOM Java Document Object Model (object/tree based)
• Lots of XML parsers and interface software available (Unix, Windows, OS/390 or Z/OS, etc.)
• SAX-based parsers are fast (often as fast as you can stream data)
• DOM slower, more memory intensive (create in-memory version of entire document)
• And, validating can be much slower than non-validating

8
XML Processing: SAX
A) SAX: Simple API for XML
– http://www.megginson.com/SAX/index.html
– An event-based interface
– Parser reports events whenever it sees a tag/attribute/text node/unresolved external
entity/other
– Programmer attaches “event handlers” to handle the event
• Advantages
– Simple to use
– Very fast (not doing very much before you get the tags and data)
– Low memory footprint (doesn’t read an XML document entirely into memory)
• Disadvantages
– Not doing very much for you -- you have to do everything yourself
– Not useful if you have to dynamically modify the document once it’s in memory (since you’ll
have to do all the work to put it in memory yourself!)

9
XML Processing: DOM
B) DOM: Document Object Model
– http://www.w3.org/DOM/
– An object-based interface
– Parser generates an in-memory tree corresponding to the document
– DOM interface defines methods for accessing and modifying the tree
• Advantages
– Very useful for dynamic modification of, access to the tree
– Useful for querying (I.e. looking for data) that depends on the tree structure
[element.childNode("2").getAttributeValue("boobie")]
– Same interface for many programming languages (C++, Java, ...)
• Disadvantages
– Can be slow (needs to produce the tree), and may need lots of memory
– DOM programming interface is a bit awkward, not terribly object oriented

10
DOM Parser Processing Model
XML data
parser
parser
interface
application
text
partorders
order
order
desc
part
quantity
delivery-date
Document “object”
DOM

11
XML Processing: JDOMC) JDOM: Java Document Object Model
– http://www.jdom.org
– A Java-specific object-oriented interface
– Parser generates an in-memory tree corresponding to the document
– JDOM interface has methods for accessing and modifying the tree
• Advantages
– Very useful for dynamic modification of the tree
– Useful for querying (I.e. looking for data) that depends on the tree structure
– Much nicer Object Oriented programming interface than DOM
• Disadvantages
– Can be slow (make that tree...), and can take up lots of memory
– New, and not entirely cooked (but close)
– Only works with Java, and not (yet) part of Core Java standard

12
XML Processing: dom4jC) dom4j: XML framework for Java
– http://www.dom4j.org
– Java framework for reading, writing, navigating and editing XML.
– Provides access to SAX, DOM, JDOM interfaces, and other XML utilities (XSLT, JAXP, …)
– Can do “mixed” SAX/DOM parsing -- use SAX to one point in a document, then turn rest into a
DOM tree.
• Advantages
– Lots of goodies, all rolled into one easy-to-use Java package
– Can do “mixed” SAX/DOM parsing -- use SAX to one point in a document, then turn rest into a
DOM tree
– Apache open source license means free use (and IBM likes it!)
• Disadvantages
– Java only; may be concerns over open source nature (but IBM uses it, so it can’t be that bad!)

13
Some XML Parsers (OS/390’s)
• Xerces (C++; Apache Open Source)
http://xml.apache.org/xerces-c/index.html
• XML toolkit (Java and C+++; Commercial license)
http://www-1.ibm.com/servers/eserver/zseries/software/xml/
I believe the Java version uses XML4j, IBM’s Java Parser. The
latest version is always found at:
http://www.alphaworks.ibm.com
• XML for C++ (IBM; based on Xerces; Commercial license)
http://www.alphaworks.ibm.com/tech/xml4c
• XMLBooster (parsers for COBOL, C++ …; Commercial license; don’t know much about it; OS/390? *dunno])
http://www.xmlbooster.com/
Has free trial download,: can see if it is any good ;-)
• XML4Cobol (don’t know much about it, any COBOL85 is fine)
http://www.xml4cobol.com
• www.xmlsoftware.com/parsers/ -- Good generic list of parsers

14
Some parser benchmarks:
• http://www-106.ibm.com/developerworks/xml/library/x-injava/index.html (Sept 2001)
• http://www.devsphere.com/xml/benchmark/index.html (Java) (late-2000)
• Basically
– SAX faster xDOM slower
– SAX less memory xDOM more memory
– SAX stream processing xDOM object / persistence processing
– nonvalidating is always faster than validating!

15
XML Processing: XSLT
D) XSLT eXtensible Stylesheet Language -- Transformations
– http://www.w3.org/TR/xslt
– An XML language for processing XML
– Does tree transformations -- takes XML and an XSLT style sheet as input, and produces a new
XML document with a different structure
• Advantages
– Very useful for tree transformations -- much easier than DOM or SAX for this purpose
– Can be used to query a document (XSLT pulls out the part you want)
• Disadvantages
– Can be slow for large documents or stylesheets
– Can be difficult to debug stylesheets (poor error detection; much better if you use schemas)

16
XSLT processing model
• D) XSLT Processing model
XSLT style sheet in
XML
parser
XSLT
processor
text
partorders
order
order
desc
part
quantity
delivery-date
document “objects” for
data and style sheet
XML
parser
XML data in
partorders
xza
order
foo
bee
data out (XML)
schema
schema

17
• XML processing
• XML messaging

18
XML Messaging• Use XML as the format for sending messages between systems
• Advantages are:
– Common syntax; self-describing (easier to parse)
– Can use common/existing transport mechanisms to “move” the XML data (HTTP, HTTPS, SMTP (email),
MQ, IIOP/(CORBA), JMS, ….)
• Requirements
– Shared understanding of dialects for transport (required registry [namespace!] ) for identifying dialects
– Shared acceptance of messaging contract
• Disadvantages
– Asynchronous transport; no guarantee of delivery, no guarantee that partner (external) shares
acceptance of contract.
– Messages will be much larger than binary (10x or more) [can compress]

19
Common messaging model
• XML over HTTP
– Use HTTP to transport XML messages
–
POST /path/to/interface.pl HTTP/1.1
Referer: http://www.foo.org/myClient.html
User-agent: db-server-olk
Accept-encoding: gzip
Accept-charset: iso-8859-1, utf-8, ucs
Content-type: application/xml; charset=utf-8
Content-length: 13221
. . .
<?xml version=“1.0” encoding=“utf-8” ?>
<message> . . . Markup in message . . .
</message>

20
Some standards for message format
• Define dialects designed to “wrap” remote invocation messages
• XML-RPC http://www.xmlrpc.com
– Very simple way of encoding function/method call name, and passed
parameters, in an XML message.
• SOAP (Simple object access protocol) http://www.soapware.org
– More complex wrapper, which lets you specify schemas for interfaces; more
complex rules for handling/proxying messages, etc. This is a core component
of Microsoft’s .NET strategy, and is integrated into more recent versions of
Websphere and other commercial packages.

21
XML Messaging + Processing
Factory
Supplier
Supplier
Supplier
Place order
(XML/edi) using
SOAP over HTTP
Response
(XML/edi) using
SOAP over HTTP
SOAP interface
SOAP
Transport
XML/
EDI
HTTP(S)
SMTP
other ...
Application
SOAP API
• XML as a universal format for data exchange

22
• XML processing
• XML messaging
• Conclusions

23
SAX 1
XML (and related) Specifications
XML 1.0 XML names
Xpath
XSLT
XSL
DOM 1
‘Open’ std
MathML
SMIL 1 & 2
SVG
XHTML 1.0
Modularized
XHTML
XHTML
basic
Xforms
Canonical
XML
signature
XML base
Xlink
Xpointer
XML query ….
Infoset
XML schema
RDF
Xfragment
XHTML
events
SOAP
UDDI FinXML
dirXML
XML-RPC
100's more ....
SAX 2
DOM 2
DOM 3
CSS 1
CSS 2
CSS 3
JDOM
JAXP
WSDL
IFX
FpML ...
ebXML
Biztalk
WDDX XMI
...
...
APIs
Style Protocols Web Services Application areas
XML Core
W3C rec
W3C draft
industry std
…...

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