Db lec 05_new

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Dr Ramadan Babers
Faculty of Science - Helwan University
Fall 2018
D B
LEC-05

1- Data Model
2
 A collection of concepts that can be used to define
the DB structure (data items& types, relationships,
operations, behavior, and constraints).
 Some Data Models:
 Entity Relationship model
 Relational Model
 hierarchical & network models
 object-data models

3- Categories of Data Models
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 Conceptual (high-level, semantic) data models:
 Provide concepts that are close to the way many users
perceive data.
 (Also called entity-based or object-based data
models.)
 Implementation (representational) data models:
 Provide concepts that fall between the above and below,
used by many commercial DBMS implementations (e.g.
relational data models used in many commercial
systems).
 Physical (low-level, internal) data models:
 Provide concepts that describe details of how data is
stored in the computer. These are usually specified in an
ad-hoc manner through DBMS design and
administration manuals

3- Categories of Data Models (cont.)
5

4- Classification of DBMSs
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 Data Model Classification
 relational,
 network,
 hierarchical,
 object-oriented
 Number of users
 single user or multi-user
 Number of Sites
 centralized vs distributed
 Cost of the DBMS
Data Model
Number of
users
Number of
sites
Cost of the
DBMS

5- System Catalog
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 Repository of information (metadata) describing
the data in the database.
 One of the fundamental components of DBMS.
 Typically stores:
 names, types, and sizes of data items;
 constraints on the data;
 names of authorized users;
 data items accessible by a user and the type of access;
 usage statistics.

6- Multi-User DBMS Architectures
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1- Teleprocessing
2- File-server
3- Client-server
A- Two-Tier
B- Three-Tier

6-1 Teleprocessing
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 Traditional architecture.
 Single mainframe with a
number of terminals
attached.
Mainframe
Terminals

6-2 File-Server
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 File-server is connected to several
workstations across a network.
 Database resides on file-server.
 DBMS and applications run on each workstation.
 Disadvantages include:
 Significant network traffic.
 Copy of DBMS on each workstation.
 Concurrency, recovery and integrity control more complex.

6-2 File-Server Architecture (cont.)
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DBMS &
Applications
Database
resides on
file-server

6-3 Client-Server
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A- Traditional Two-Tier
 Client (tier 1) manages user interface and runs
applications.
 Server (tier 2) holds database and DBMS.
 Advantages include:
 wider access to existing databases;
 increased performance;
 possible reduction in hardware costs;
 reduction in communication costs;
 increased consistency.

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Traditional
Two-Tier
Client-Server
6-3 Client-Server (cont.)
Tier-2
Database &
DBMS
Tier-1
User interface
& applications

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B- Three-Tier
 Client side presented two problems preventing
true scalability:
 ‘Fat’ client, requiring considerable resources on client’s
computer to run effectively.
 Significant client side administration overhead.
 By 1995, three layers proposed, each
potentially running on a different platform.

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 Advantages:
‘Thin’ client, requiring less expensive hardware.
Application maintenance centralized.
Easier to modify or replace onetier without
affecting others.
Separating business logic from database functions
makes it easier to implement load balancing.

Three-Tier Client-Server
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7- Transaction Processing Monitors
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 Program that controls data transfer
between clients and servers in order to
provide a consistent environment,
particularly for Online Transaction
Processing (OLTP).
 Online Analytical Processing (OLAP).

TPM as middle tier of 3-tier client-server
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Db lec 05_new

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