Ch#6,SWE211

Architectural design

creative process so the process differs depending on the type of system being developed.

Patterns should include

information about when they are and when the are not useful.

software architecture

is a description of how a software system is organized. Properties of a system such as performance, security, and availability are influenced by the architecture used.

Example of Layered architecture pattern

layered model of a system for sharing copyright documents held in different libraries,

how many views does the architectural model shows?

one view or perspective of the system.

Physical view

System engineering - System topology - Delivery and installation - Communication

Process view

System integrators - Performance - Scalability - Throughput

Architecture and system characteristics

(non-functional requirements) -Performance (نحدد اجزاء كبيرة) -Security( الأشياء المهمة تكون في الطبقات الداخلية) -Safety (critical features) -Availability -Maintainability (replaceable components)

Description of Layered architecture pattern

- Organizes the system into layers with related functionality associated with each layer. - A layer provides services to the layer above it so the lowest-level layers represent core services that are likely to be used throughout the system.

architectural design

- early stage of the system design process. - link between specification and design processes. - Often carried out in parallel with some specification activities. -involves identifying major system components and their communications.

When to use Repository Pattern?

- system in which large volumes of information are generated that has to be stored for a long time. - data-driven systems where the inclusion of data in the repository triggers an action or tool.

Description of Repository Pattern

-All data in a system is managed in a central repository that is accessible to all system components. -Components do not interact directly, only through the repository

Advantages of Repository Pattern

-Components can be independent—they do not need to know of the existence of other components. -Changes made by one component can be propagated to all components. -All data can be managed consistently (e.g., backups done at the same time) as it is all in one place.

Client-server architecture

-Distributed system model which shows how data and processing is distributed across a range of components. -Set of stand-alone servers which provide specific services such as printing, data management, etc. -Set of clients which call on these services. -Network which allows clients to access servers.

Disadvantages of Client-server pattern

-Each service is a single point of failure so susceptible to denial of service attacks or server failure. -Performance may be unpredictable because it depends on the network as well as the system. -May be management problems if servers are owned by different organizations.

Sub-systems must exchange data. This may be done in two ways:

-Shared data is held in a central database or repository and may be accessed by all sub-systems -Each sub-system maintains its own database and passes data explicitly to other sub-systems.

Box and line diagrams

-Simple -Very abstract عام مايبيّن تفاصيل كثير -Depends on the use of architectural models

advantages of explicit architecture

-Stakeholder communication -System analysis -Large-scale reuse

Architecture reuse

-Systems in the same domain often have similar architectures -architecture of a system may be designed around one of more architectural patterns or 'styles'.

Layered Architecture

-Used to model the interfacing of sub-systems. -Organises the system into a set of layers (or abstract machines) -Supports the incremental development of sub-systems(When a layer interface changes, only the adjacent layer is affected)

4 + 1 view

-logical view (key abstractions in the system as objects or object classes.) -process view (system is composed of interacting processes.) -development view (software is decomposed for development.) -physical view (system hardware) +1 (use cases or scenarios)

Disadvantages of Layered architecture pattern

-providing a clean separation between layers is often difficult and a high-level layer may have to interact directly with lower-level layers rather than through the layer immediately below it. -Performance can be a problem because of multiple levels of interpretation of a service request as it is processed at each layer.

Disadvantages of Repository Pattern

-repository is a single point of failure so problems in the repository affect the whole system. -May be inefficiencies in organizing all communication through the repository. - Distributing the repository across several computers may be difficult.

Large-scale reuse

-the architecture may be reusable across a range of systems -Product-line architectures may be developed.

Description of Client-server pattern

-the functionality of the system is organized into services, with each service delivered from a separate server. -Clients are users of these services and access servers to make use of them.

When to use Layered architecture pattern?

-when building new facilities on top of existing systems; -when the development is spread across several teams with each team responsibility for a layer of functionality; -when there is a requirement for multi-level security.

When to use Client-server pattern?

-when data in a shared database has to be accessed from a range of locations. Because servers can be replicated, may also be used when the load on a system is variable.

Application Architectures

A-pplication systems are designed to meet an organizational need. -As businesses have much in common, their application systems also tend to have a common architecture that reflects the application requirements. -A generic application architecture is an architecture for a type of software system that may be configured and adapted to create a system that meets specific requirements.

Advantages of Layered architecture pattern

Allows replacement of entire layers so long as the interface is maintained. Redundant facilities (e.g., authentication) can be provided in each layer to increase the dependability of the system.

Use case view

Analysts/Testers - Behavior

Event processing systems

Applications where system actions depend on interpreting events from the system's environment.

Language processing systems

Applications where the users' intentions are specified in a formal language that is processed and interpreted by the system. -Accept a natural or artificial language as input and generate some other representation of that language. -May include an interpreter to act on the instructions in the language that is being processed. -Used in situations where the easiest way to solve a problem is to describe an algorithm or describe the system data like: Compilers; Command interpreters.

Stakeholder communication

Architecture may be used as a focus of discussion by system stakeholders.

Data processing applications

Data driven applications that process data in batches without explicit user intervention during the processing.

Transaction processing applications

Data-centred applications that process user requests and update information in a system database.

Logical view

End user - Functionality - Vocabulary

Example of Repository Pattern

IDE where the components use a repository of system design information. Each software tool generates information which is then available for use by other tools.(page32)

Detailed Design

It defines logical structure of each module and their interfaces to communicate with other modules.

System analysis

Means that analysis of whether the system can meet its non-functional requirements is possible.

Commonly used architectural patterns include

Model-View-Controller, Layered Architecture, Repository, Client-server, and Pipe and Filter.

Development view

Programmers - Software management

architectural design

The design process for identifying the sub-systems making up a system and the framework for sub-system control and communication

software architecture.

The output of this design process is a description of .....

Possible views include

a conceptual view, a logical view, a process view, a development view, and a physical view.

Patterns

are a means of representing, sharing and reusing knowledge.

Architectural patterns

are a means of reusing knowledge about generic system architectures. They describe the architecture, explain when it may be used, and discuss its advantages and disadvantages.

Transaction processing systems

are interactive systems that allow information in a database to be remotely accessed and modified by a number of users. Information systems and resource management systems are examples of transaction processing systems.

Language processing systems

are used to translate texts from one language into another and to carry out the instructions specified in the input language. They include a translator and an abstract machine that executes the generated language.

High-level Architectural Design

breaks the 'single entity-multiple component' concept of architectural design into less-abstracted view of sub-systems and modules and depicts their interaction with each other. It recognizes modular structure of each sub-system and their relation and interaction among each other.

Detailed Design

deals with the implementation part of what is seen as a system and its sub-systems in the previous design.

The output of software design process is

design documentation, pseudo codes, detailed logic diagrams, process diagrams, and detailed description of all functional or non-functional requirements.

Architectures may be

documented from several different perspectives or views.

Example of Client-server pattern

film and video/DVD library organized as a client-server system. (page35)

Generic models of application systems architectures

help us understand the operation of applications, compare applications of the same type, validate application system designs, and assess large-scale components for reuse.

High-level design focuses on

how the system along with all of its components can be implemented in forms of modules

Architectural design decisions

include decisions on the type of application, the distribution of the system, the architectural styles to be used, and the ways in which the architecture should be documented and evaluated.

Advantages of Client-server pattern

servers can be distributed across a network. General functionality (e.g., a printing service) can be available to all clients and does not need to be implemented by all services.

Architectural Pattern

stylized description of good design practice, which has been tried and tested in different environments.

Patterns may be represented using

tabular and graphical descriptions.

When large amounts of data are to be shared

the repository model of sharing is most commonly used a this is an efficient data sharing mechanism.

Application Types

▶ Data processing applications ▶ Transaction processing applications ▶ Event processing systems ▶ Language processing systems

Compiler Components

▶A lexical analyzer, which takes input language tokens and converts them to an internal form. ▶A symbol table, which holds information about the names of entities (variables, class names, object names, etc.) used in the text that is being translated. ▶A syntax analyzer, which checks the syntax of the language being translated. ▶A syntax tree, which is an internal structure representing the program being compiled. ▶A semantic analyzer that uses information from the syntax tree and the symbol table to check the semantic correctness of the input language text. ▶A code generator that 'walks' the syntax tree and generates abstract machine code.

Use of Application Architectures

▶As a starting point for architectural design. ▶ As a design checklist. ▶ As a way of organising the work of the development team. ▶ As a means of assessing components for reuse. ▶ As a vocabulary for talking about application types.