Week6Architectural designfocusedv2.pdf

Architectural Design 24/10/2023 Chapter 6 Architectural Design 1 Architectural design considerations    Architectural design is concerned with understanding how a software system should be organized and designing the overall structure of that system. Architectural design is the critical l...

Architectural Design 24/10/2023 Chapter 6 Architectural Design 1 Architectural design considerations    Architectural design is concerned with understanding how a software system should be organized and designing the overall structure of that system. Architectural design is the critical link between design and requirements engineering, as it identifies the main structural components in a system and the relationships between them. The output of the architectural design process is an architectural model that describes how the system is organized as a set of communicating components. 24/10/2023 Chapter 6 Architectural Design 2 Example N-tier Architecture (Using Java Technology) Web Tier EJB Tier Agility and architecture It is generally accepted that an early stage of agile processes is to design an overall systems architecture.  Refactoring the system architecture is usually expensive because it affects so many components in the system  24/10/2023 Chapter 6 Architectural Design 4 Architectural abstraction   Architecture in the small is concerned with the architecture of individual programs. At this level, we are concerned with the way that an individual program is decomposed into components. Architecture in the large is concerned with the architecture of complex enterprise systems that include other systems, programs, and program components. These enterprise systems are distributed over different computers, which may be owned and managed by different companies. 24/10/2023 Chapter 6 Architectural Design 5 Advantages of explicit architecture  Stakeholder communication ◦ Architecture may be used as a focus of discussion by system stakeholders.  System analysis ◦ Means that analysis of whether the system can meet its non-functional requirements is possible.  Large-scale reuse ◦ The architecture may be reusable across a range of systems ◦ Product-line architectures may be developed. 24/10/2023 Chapter 6 Architectural Design 6 Architectural representations    Simple, informal block diagrams showing entities and relationships are the most frequently used method for documenting software architectures. But these have been criticised because they lack semantics, do not show the types of relationships between entities nor the visible properties of entities in the architecture. Depends on the use of architectural models. The requirements for model semantics depends on how the models are used. 24/10/2023 Chapter 6 Architectural Design 7 Box and line diagrams Very abstract - they do not show the nature of component relationships nor the externally visible properties of the sub-systems.  However, useful for communication with stakeholders and for project planning.  24/10/2023 Chapter 6 Architectural Design 8 Use of architectural models  As a way of facilitating discussion about the system design ◦ A high-level architectural view of a system is useful for communication with system stakeholders and project planning because it is not cluttered with detail. Stakeholders can relate to it and understand an abstract view of the system. They can then discuss the system as a whole without being confused by detail.  As a way of documenting an architecture that has been designed ◦ The aim here is to produce a complete system model that shows the different components in a system, their interfaces and their connections. 24/10/2023 Chapter 6 Architectural Design 9 Architectural patterns 24/10/2023 Chapter 6 Architectural Design 10 Architectural patterns considerations Patterns are a means of representing, sharing and reusing knowledge.  An architectural pattern is a stylized description of good design practice, which has been tried and tested in different environments.  Patterns should include information about when they are and when the are not useful.  Patterns may be represented using tabular and graphical descriptions.  24/10/2023 Chapter 6 Architectural Design 11 Layered architecture     Used to model the interfacing of sub-systems. Organises the system into a set of layers (or abstract machines) each of which provide a set of services. Supports the incremental development of sub-systems in different layers. When a layer interface changes, only the adjacent layer is affected. However, often artificial to structure systems in this way. 24/10/2023 Chapter 6 Architectural Design 12 A generic layered architecture 24/10/2023 Chapter 6 Architectural Design 13 The Layered architecture pattern Name Layered architecture Description 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. See Figure 6.6. A layered model of a system for sharing copyright documents held in different libraries, as shown in Figure 6.7. Used 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. 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. In practice, 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. Example When used Advantages Disadvantages 24/10/2023 Chapter 6 Architectural Design 14 The architecture of the iLearn system 24/10/2023 Chapter 6 Architectural Design 15 Client-server architecture  Distributed system model which shows how data and processing is distributed across a range of components. ◦ Can be implemented on a single computer. 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.  24/10/2023 Chapter 6 Architectural Design 16 The Client–server pattern Name Client-server Description In a client–server architecture, 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. Figure 6.11 is an example of a film and video/DVD library organized as a client–server system. Used 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. The principal advantage of this model is that 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. 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. Example When used Advantages Disadvantages 24/10/2023 Chapter 6 Architectural Design 17 A client–server architecture for a film library 24/10/2023 Chapter 6 Architectural Design 18 Application architectures 24/10/2023 Chapter 6 Architectural Design 19 Application architectures considerations    Application 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. 24/10/2023 Chapter 6 Architectural Design 20 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.  24/10/2023 Chapter 6 Architectural Design 21 Examples of application types  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.  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. 24/10/2023 Chapter 6 Architectural Design 22 Application type examples   Two very widely used generic application architectures are transaction processing systems and language processing systems. Transaction processing systems ◦ E-commerce systems; ◦ Reservation systems.  Language processing systems ◦ Compilers; ◦ Command interpreters. 24/10/2023 Chapter 6 Architectural Design 23 Transaction processing systems Process user requests for information from a database or requests to update the database.  From a user perspective a transaction is:  ◦ Any coherent sequence of operations that satisfies a goal;  Users make asynchronous requests for service which are then processed by a transaction manager. 24/10/2023 Chapter 6 Architectural Design 24 The structure of transaction processing applications 24/10/2023 Chapter 6 Architectural Design 25 The software architecture of an ATM system 24/10/2023 Chapter 6 Architectural Design 26 Information systems architecture    Information systems have a generic architecture that can be organized as a layered architecture. These are transaction-based systems as interaction with these systems generally involves database transactions. Layers include: ◦ ◦ ◦ ◦ The user interface User communications Information retrieval System database 24/10/2023 Chapter 6 Architectural Design 27 Layered information system architecture 24/10/2023 Chapter 6 Architectural Design 28 The architecture of the Mentcare system 24/10/2023 Chapter 6 Architectural Design 29 Web-based information systems Information and resource management systems are now usually web-based systems where the user interfaces are implemented using a web browser.  For example, e-commerce systems are Internet-based resource management systems that accept electronic orders for goods or services and then arrange delivery of these goods or services to the customer.  In an e-commerce system, the application-specific layer includes additional functionality supporting a ‘shopping cart’ in which users can place a number of items in separate transactions, then pay for them all together in a single transaction.  24/10/2023 Chapter 6 Architectural Design 30 Server implementation  These systems are often implemented as multi-tier client server/architectures ◦ The web server is responsible for all user communications, with the user interface implemented using a web browser; ◦ The application server is responsible for implementing application-specific logic as well as information storage and retrieval requests; ◦ The database server moves information to and from the database and handles transaction management. 24/10/2023 Chapter 6 Architectural Design 31 Key points 1 A software architecture is a description of how a software system is organized.  Architectural design decisions include decisions on the type of application, the distribution of the system, the architectural styles to be used.  Architectures may be documented from several different perspectives or views such as a conceptual view, a logical view, a process view, and a development view.  Architectural patterns are a means of reusing knowledge about generic system architectures. They describe the architecture, explain when it may be used and describe its advantages and disadvantages.  24/10/2023 Chapter 6 Architectural Design 32 Key points 2 Models of application systems architectures help us understand and compare applications, validate application system designs and assess large-scale components for reuse.  Transaction processing systems are interactive systems that allow information in a database to be remotely accessed and modified by a number of users.  24/10/2023 Chapter 6 Architectural Design 33