CSC440 Chapter 15: Software Reuse (Software Engineering, Sommerville, 10th Edition)

ERP Architecture

- A number of modules to support different business functions. - A defined set of business processes, associated with each module, which relate to activities in that module. - A common database that maintains information about all related business functions. - A set of business rules that apply to all data in the database.

Benefits of Software Reuse

- Accelerated development - Effective use of specialists - Increased dependability - Lower Development costs - Reduced process risk - Standards compliance

ERP Systems

- An Enterprise Resource Planning (ERP) system is a generic system that supports common business processes such as ordering and invoicing, manufacturing, etc. - These are very widely used in large companies - they represent probably the most common form of software reuse. - The generic core is adapted by including modules and by incorporating knowledge of business processes and rules.

Approaches that Support Software Reuse

- Application frameworks - Application System Integration - Architectural Patterns - Aspect-Oriented Software Development - Component-based Software Development - Configurable Application Systems - Design Patterns - ERP Systems - Legacy System Wrapping - Model-Driven Engineering - Program Generators - Program Libraries - Service-Orientated Systems - Software Product Lines - Systems of Systems

Service-Oriented Interfaces

- Application system integration can be simplified if a service-oriented approach is used. - A service-oriented approach means allowing access to the application system's functionality through a standard service interface, with a service for each discrete unit of functionality. - Some applications may offer a service interface but, sometimes, this service interface has to be implemented by the system integrator. You have to program a wrapper that hides the application and provides externally visible services.

Application System Reuse

- Application system product is a software system that can be adapted for different customers without changing the source code of the system - Application systems have generic features so can be used/reused in different environments. Products adapted by using built in configuration mechanisms. - Allow functionality of the system to be tailored

Integrated Application Systems

- Applications that include two or more application system products and/or legacy application systems. - You may use this approach when there is no single application system that meets all of your needs or when you wish to integrate a new application system with systems that you already use.

Configurable Application Systems

- Configurable application systems are generic application systems that may be designed to support a particular business type - Domain-specific systems, such as systems to support a business function (e.g. document management) provide functionality that is likely to be required by a range of potential users.

Problems with Software Reuse

- Creating, Maintaining and using a component library - Finding, understanding and adapting reusable components - Increased maintenance costs - Lack of tool support - Not-invented-here syndrome (Also means lack of documentation)

Application system integration problems

- Lack of control over functionality and performance: Application systems may be less effective than they appear - Problems with application system inter-operability: Different application systems may make different assumptions that means integration is difficult - No control over system evolution: Application system vendors not system users control evolution - Support from system vendors: Application system vendors may not offer support over the lifetime of the product

Application Frameworks

- Moderately large entities that can be reused - Sub-system design made up of a collection of abstract and concrete classes and the interfaces between them. - Sub-system is implemented by adding components to fill in parts of the design and by instantiating the abstract classes in the framework.

Benefits of Application System Reuse

- More rapid deployment - See what functionality is provided - Development risks are avoided by using existing software - Businesses can focus on core activity w/out having to devote IT resources - Updates can be simplified

Product Line Specialization

- Platform specialization: Different versions for different platforms - Environment specialization: Different versions created to handle different environments - Functional specialization: Different versions created for different requirements - Process specialization: Different versions created to support different business processes

Problems of Application System Reuse

- Requirements usually need to be adapted - COTS product may be based on assumptions - Choosing the right COTS system for an enterprise can be difficult - Lack of local expertise to support systems - COTS product vendor controls system support and evolution

WAF Features

- Security: WAFs may include classes to help implement user authentication (login) and access. - Dynamic web pages: Classes are provided to help you define web page templates and to populate these dynamically from the system database. - Database support: The framework may provide classes that provide an abstract interface to different databases. - Session management: Classes to create and manage sessions (a number of interactions with the system by a user) are usually part of a WAF. - User interaction: Most web frameworks now provide AJAX support, which allows more interactive web pages to be created.

Key Points (cont.)

- Software product lines are related applications that are developed from one or more base applications. A generic system is adapted and specialized to meet specific requirements for functionality, target platform or operational configuration. - Application system reuse is concerned with the reuse of large-scale, off-the-shelf systems. These provide a lot of functionality and their reuse can radically reduce costs and development time. Systems may be developed by configuring a single, generic application system or by integrating two or more application systems. - Potential problems with application system reuse include lack of control over functionality and performance, lack of control over system evolution, the need for support from external vendors and difficulties in ensuring that systems can inter-operate.

Software Product Lines

- Software product lines or application families are applications with generic functionality that can be adapted and configured for use in a specific context. - Set of applications with a common architecture and shared components

Web Application Frameworks

- Support the construction of dynamic websites as a front-end for web applications. - WAFs are now available for all of the commonly used web programming languages e.g. Java, Python, Ruby, etc. - Interaction model is based on the Model-View-Controller composite pattern.

Model-View-Controller

- System infrastructure framework for GUI design. - Allows for multiple presentations of an object and separate interactions with these presentations. - MVC framework involves the instantiation of a number of patterns

Framework Classes

- System infrastructure frameworks: Support the development of system infrastructures such as communications, user interfaces and compilers. - Middleware integration frameworks: Standards and classes that support component communication and information exchange. - Enterprise application frameworks: Support the development of specific types of application such as telecommunications or financial systems.

Software Reuse

- Systems are designed by composing existing components that have been used in other systems. - There has been a major switch to reuse-based development over the past 10 years.

Key Points

- There are many different ways to reuse software. These range from the reuse of classes and methods in libraries to the reuse of complete application systems. - The advantages of software reuse are lower costs, faster software development and lower risks. System dependability is increased. Specialists can be used more effectively by concentrating their expertise on the design of reusable components. - Application frameworks are collections of concrete and abstract objects that are designed for reuse through specialization and the addition of new objects. They usually incorporate good design practice through design patterns.

Levels of Deployment Time Configuration

1) Component selection: where you select the modules in a system that provide the required functionality. 2) Workflow and rule definition: where you define workflows (how information is processed, stage-by-stage) and validation rules that should apply to information entered by users or generated by the system. 3) Parameter definition: where you specify the values of specific system parameters that reflect the instance of the application that you are creating

Product Line Configuration

1) Design time configuration: Modifies a common product to create a new system for customer 2) Deployment time configuration: Generic system designed for configuration by a customer

Key factors when Determining to Reuse Software

1) Development schedule for the software 2) The expected software lifetime 3) The background, skills, and experience of the development team 4) The criticality of the software and its non-functional requirements 5) The application domain

Process for Extending a Software Product Line

1) Elicit stakeholder requirements: Use existing family member as prototype 2) Choose closest-fit family member: Member best meets the requirements 3) Re-negotiate requirements: Adapt requirements as necessary 4) Adapt existing system 5) Deliver new family member

ERP Configuration

1) Selecting the required functionality from the system. 2) Establishing a data model that defines how the organization's data will be structured in the system database. 3) Defining business rules that apply to that data. 4) Defining the expected interactions with external systems. 5) Designing the input forms and the output reports generated by the system. 6) Designing new business processes that conform to the underlying process model supported by the system. 7) Setting parameters that define how the system is deployed on its underlying platform.

Levels of Software Reuse

1) System Reuse: Complete systems, which may include several application programs may be reused. 2) Application Reuse: An application may be reused either by incorporating it without change into other or by developing application families. 3) Component Reuse: Components of an application from sub-systems to single objects may be reused. 4) Object and Function Reuse: Small-scale software components that implement a single well-defined object or function may be reused.

Definition of a Framework

An integrated set of software artifacts (such as classes, objects and components) that collaborate to provide a reusable architecture for a family of related applications.