Architec design introduction
- 1. UNIT - 3 Architectural Design - Introduction - Data design - Software architectural styles
- 2. Introduction
- 3. 3 Definitions • The software architecture of a program or computing system is the structure or structures of the system which comprise – The software components – The externally visible properties of those components – The relationships among the components • Software architectural design represents the structure of the data and program components that are required to build a computer-based system • An architectural design model is transferable – It can be applied to the design of other systems – It represents a set of abstractions that enable software engineers to describe architecture in predictable ways
- 4. 4 Architectural Design Process • Basic Steps – Creation of the data design – Derivation of one or more representations of the architectural structure of the system – Analysis of alternative architectural styles to choose the one best suited to customer requirements and quality attributes – Elaboration of the architecture based on the selected architectural style • A database designer creates the data architecture for a system to represent the data components • A system architect selects an appropriate architectural style derived during system engineering and software requirements analysis
- 5. 5 Emphasis on Software Components • A software architecture enables a software engineer to – Analyze the effectiveness of the design in meeting its stated requirements – Consider architectural alternatives at a stage when making design changes is still relatively easy – Reduce the risks associated with the construction of the software • Focus is placed on the software component – A program module – An object-oriented class – A database – Middleware
- 6. 6 Importance of Software Architecture • Representations of software architecture are an enabler for communication between all stakeholders interested in the development of a computer-based system • The software architecture highlights early design decisions that will have a profound impact on all software engineering work that follows and, as important, on the ultimate success of the system as an operational entity • The software architecture constitutes a relatively small, intellectually graspable model of how the system is structured and how its components work together
- 7. 7 Example Software Architecture Diagrams
- 8. Data Design
- 9. 9 Purpose of Data Design • Data design translates data objects defined as part of the analysis model into – Data structures at the software component level – A possible database architecture at the application level • It focuses on the representation of data structures that are directly accessed by one or more software components • The challenge is to store and retrieve the data in such way that useful information can be extracted from the data environment • "Data quality is the difference between a data warehouse and a data garbage dump"
- 10. 10 Data Design Principles • The systematic analysis principles that are applied to function and behavior should also be applied to data • All data structures and the operations to be performed on each one should be identified • A mechanism for defining the content of each data object should be established and used to define both data and the operations applied to it • Low-level data design decisions should be deferred until late in the design process • The representation of a data structure should be known only to those modules that must make direct use of the data contained within the structure • A library of useful data structures and the operations that may be applied to them should be developed • A software programming language should support the specification and realization of abstract data types
- 12. 12 Common Architectural Styles of American Homes
- 13. 13 Common Architectural Styles of American Homes A-Frame Bungalow Cape Cod Colonial Federal Four square Greek Revival Georgian Pueblo Prairie Style Ranch Split level Tidewater Victorian Tudor
- 14. 14 Software Architectural Style • The software that is built for computer-based systems exhibit one of many architectural styles • Each style describes a system category that encompasses – A set of component types that perform a function required by the system – A set of connectors (subroutine call, remote procedure call, data stream, socket) that enable communication, coordination, and cooperation among components – Semantic constraints that define how components can be integrated to form the system – A topological layout of the components indicating their runtime interrelationships
- 15. 15 A Taxonomy of Architectural Styles Independent Components Communicating Processes Event Systems Client/Server Peer-to-Peer Implicit Invocation Explicit Invocation Data Flow Batch Sequential Pipe and Filter Virtual Machine Interpreter Rule-Based System Data-Centered Repository Blackboard Call and Return Main Program and Subroutine Object OrientedLayered Remote Procedure Call
- 16. 16 Data Flow Style Validate Sort Update Report
- 17. 17 Data Flow Style • Has the goal of modifiability • Characterized by viewing the system as a series of transformations on successive pieces of input data • Data enters the system and then flows through the components one at a time until they are assigned to output or a data store • Batch sequential style – The processing steps are independent components – Each step runs to completion before the next step begins • Pipe-and-filter style – Emphasizes the incremental transformation of data by successive components – The filters incrementally transform the data (entering and exiting via streams) – The filters use little contextual information and retain no state between instantiations – The pipes are stateless and simply exist to move data between filters (More on next slide)
- 18. 18 Data Flow Style (continued) • Advantages – Has a simplistic design in the limited ways in which the components interact with the environment – Consists of no more and no less than the construction of its parts – Simplifies reuse and maintenance – Is easily made into a parallel or distributed execution in order to enhance system performance • Disadvantages – Implicitly encourages a batch mentality so interactive applications are difficult to create in this style – Ordering of filters can be difficult to maintain so the filters cannot cooperatively interact to solve a problem – Exhibits poor performance • Filters typically force the least common denominator of data representation (usually ASCII stream) • Filter may need unlimited buffers if they cannot start producing output until they receive all of the input • Each filter operates as a separate process or procedure call, thus incurring overhead in set-up and take-down time (More on next slide)
- 19. 19 Data Flow Style (continued) • Use this style when it makes sense to view your system as one that produces a well-defined easily identified output – The output should be a direct result of sequentially transforming a well- defined easily identified input in a time-independent fashion
- 20. 20 Call-and-Return Style Main module Subroutine A Subroutine B Subroutine A-1 Subroutine A-2 Physical layer Data layer Network layer Transport layer Application layer Class WClass V Class X Class Z Class Y
- 21. 21 Call-and-Return Style • Has the goal of modifiability and scalability • Has been the dominant architecture since the start of software development • Main program and subroutine style – Decomposes a program hierarchically into small pieces (i.e., modules) – Typically has a single thread of control that travels through various components in the hierarchy • Remote procedure call style – Consists of main program and subroutine style of system that is decomposed into parts that are resident on computers connected via a network – Strives to increase performance by distributing the computations and taking advantage of multiple processors – Incurs a finite communication time between subroutine call and response
- 22. 22 Call-and-Return Style (continued) • Object-oriented or abstract data type system – Emphasizes the bundling of data and how to manipulate and access data – Keeps the internal data representation hidden and allows access to the object only through provided operations – Permits inheritance and polymorphism • Layered system – Assigns components to layers in order to control inter-component interaction – Only allows a layer to communicate with its immediate neighbor – Assigns core functionality such as hardware interfacing or system kernel operations to the lowest layer – Builds each successive layer on its predecessor, hiding the lower layer and providing services for the upper layer – Is compromised by layer bridging that skips one or more layers to improve runtime performance • Use this style when the order of computation is fixed, when interfaces are specific, and when components can make no useful progress while awaiting the results of request to other components
- 23. 23 Data-Centered Style Shared Data Client A Client B Client C Client D Client E Client F
- 24. 24 Data-Centered Style (continued) • Has the goal of integrating the data • Refers to systems in which the access and update of a widely accessed data store occur • A client runs on an independent thread of control • The shared data may be a passive repository or an active blackboard – A blackboard notifies subscriber clients when changes occur in data of interest • At its heart is a centralized data store that communicates with a number of clients • Clients are relatively independent of each other so they can be added, removed, or changed in functionality • The data store is independent of the clients
- 25. 25 Data-Centered Style (continued) • Use this style when a central issue is the storage, representation, management, and retrieval of a large amount of related persistent data • Note that this style becomes client/server if the clients are modeled as independent processes
- 26. 26 Heterogeneous Styles • Systems are seldom built from a single architectural style • Three kinds of heterogeneity – Locationally heterogeneous • The drawing of the architecture reveals different styles in different areas (e.g., a branch of a call-and-return system may have a shared repository) – Hierarchically heterogeneous • A component of one style, when decomposed, is structured according to the rules of a different style – Simultaneously heterogeneous • Two or more architectural styles may both be appropriate descriptions for the style used by a computer-based system
- 27. 27 Summary • A software architecture provides a uniform, high-level view of the system to be built • It depicts – The structure and organization of the software components – The properties of the components – The relationships (i.e., connections) among the components • Software components include program modules and the various data representations that are manipulated by the program • The choice of a software architecture highlights early design decisions and provides a mechanism for considering the benefits of alternative architectures • Data design translates the data objects defined in the analysis model into data structures that reside in the software (More on next slide)
- 28. 28 Summary (continued) • A number of different architectural styles are available that encompass a set of component types, a set of connectors, semantic constraints, and a topological layout • The architectural design process contains four distinct steps 1) Represent the system in context 2) Identify the component archetypes (the top-level abstractions) 3) Identify and refine components within the context of various architectural styles 4) Formulate a specific instantiation of the architecture • Once a software architecture has been derived, it is elaborated and then analyzed against quality criteria