1. Software Engineering Architectural Design Chapter 6 Dr.Doaa Sami
Modified from Sommerville’s originals

2. Objectives  Understand the importance of architectural design.2
 Understand the importance of architectural design.
 Introduce to the architectural views.
 Understand the decisions that be made during architectural design.
 Know the architectural patterns that are often used in different types of application system.

3. Architecture 3
 Architecture: Floor plan

4. Software Design The software design process is composed of four main4
The software design process is composed of four main
design activities:
 Architectural design  this chapter.
 Data design.
 Component design.
 Interface design.

5. Software Design Deliverables5
The main deliverables of the Software Design are:
 Software architecture.
 Data structures.
 Pseudo code.
 Interface designs.
 Software Design Document.

6. Software Architecture6
 Architectural Design: The design process concerned with understanding how a system should be organized and designing the overall structure of that system.
 Software Architecture model: Output of this design process, describes how the system is organized as a set of communicating components.
 A Software Architecture consists of:
 Elements (components) with certain properties/behaviors.
 Relationships between them.
 Description of permitted and forbidden interactions.

7. Architectural Design 7
 It is the first stage in the software design process.
 It links between specification and design process.
 Often carried out in parallel with some of the specification activities. However, this is not ideally.
 It involves identifying main structural components in a system and the relationships between them.

8. Architecture and System Characteristics13
A particular architectural style that you choose for a system should depend on the non-functional requirements (System Characteristics):
 Performance
 If it is critical, use large and few components  less communications.
 Security
 If it is critical, use a layered architecture with critical assets in the innermost layer with high level of validation in this layer.
 Safety
 If it is critical, put safety-critical features in one or small number of sub- systems to reduces costs in the event of failure.
 Availability
 If it is critical, include redundant components  update without stop.
 Maintainability
 If it is critical, use separate components and avoid shared data structure.

9. 1. System Organization system.17
 Reflects the basic strategy that is used to organize a
system.
 Three architectural styles are widely used:
 An abstract machine or layered style;
 A shared data repository style;
 A client/server style.

10. Layered Architecture  Used to model the interfacing of sub-systems.18
 Used to model the interfacing of sub-systems.
 Organizes 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.
 Each layer provides a set of services to the layer above and serves as a client to the layer below.

11. Layered Architecture 19

12. The Architecture of the LIBSYS System20

13. Advantages & Disadvantages of Layered Style21
 Advantages:
 Supports incremental development.
 Changeable (if a layer changes, only adjacent layers are affected).
 Disadvantages:
 Structuring systems into layers is difficult.
 Inner layers may provides facilities required by all layers (e.g. file management).
 Performance is degraded.

14. Repository Style  Sub-systems must exchange data.22
 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.
 When?
 large amounts of data are to be shared, the repository model of sharing is most commonly used.

15. Advantages & Disadvantages of Repository Style23
 Advantages:
 Efficient way to share large amounts of data;
 Sub-systems need not be concerned with how data is produced;
 Centralized management e.g. backup, security, etc.
 Sharing model is published as the repository schema.
 Disadvantages:
 Sub-systems must agree on a repository data model;
 Data evolution is difficult and expensive;
 No scope for specific management policies;
 Difficult to distribute efficiently.

16. Repository Style for Project24

17. Client-Server Architecture25
 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.
 Client and server exchange data for processing.

18.  Advantages:  Disadvantages:
Advantages & Disadvantages of Client–Server 26
 Advantages:
 Servers can be distributed across a network.
 General functionality (e.g. printing service) can be available to all clients and does not need to be implemented by all services.
 Easy add new server or upgrade existing one.
 Disadvantages:
 Security problem, each server will be suspected if a fault happen.
 Performance may be unpredictable because it depends on the
network as well as the system.
 Management problems with servers owned by different organizations.

19. Client–Server Architecture for a Film Library27