Software Engineering

Transcription

1 Software Engineering A systematic approach to the analysis, design, implementation and maintenance of software. Software Development Method by Jan Pettersen Nytun, page 1

2 Software Engineering Methods Most methods consist of both a modelling language and a process (who is doing what and when). The modelling language - the notation - typically includes some visual language (different types of diagrams). A tool to support the method is also crucial. Software Development Method by Jan Pettersen Nytun, page 2

3 UML Is Not a Process The UML is intentionally process independent - Different domain may require different processes. But the UML authors promote a development process that is (examples of methods: The Unified Software Development Process and RUP) use-case-driven incremental and iterative architecture centric Software Development Method by Jan Pettersen Nytun, page 3

4 Software Development Two Processes at the Same Time The Management Process - schedules work, deliveries and resources, monitor progress. The management process is controlling The Development Process which is about developing software from requirements. Some methods contains both processes, e.g. RUP; others are mostly development processes, like Catalysis, and others again are management processes, e.g. Dynamic Systems Development Method (DSDM). Software Development Method by Jan Pettersen Nytun, page 4

5 Heavy-weight And Lightweight Software Processes Heavy-weight: many rules, practices and documents. Example: Standard RUP (RUP can also be adapted to be a light-weight process). Light-weight: few rules and practices or some that are easy to follow. Agile processes are examples of light-weight processes: Customer collaboration, responding to change, and focus on working software over documentation. Software Development Method by Jan Pettersen Nytun, page 5

6 Software Process Models The waterfall model (the original version): Requirements are defined first and each phase is ended before moving to the next phase. Evolutionary, incremental and iterative development: Requirements are covered gradually and the system is delivered in releases. Software Development Method by Jan Pettersen Nytun, page 6

7 Requirements Analysis and Capture Purpose: Understand the problem domain and the system to be implemented; communicate with end users and document the requirements. The waterfall model of software development Design Purpose: Transform the products of the analysis phase into a more precise description that can be refined into an executable program. Implementation Purpose: Transform the products of the design phase into concepts that can be executed on the computer. Unit testing. Testing and Integration System Testing Operation and Maintenance

8 Requirements Analysis and Capture - 1 A requirement is a wanted property or behavior of a system. There are two types of requirements: Functional Nonfunctional From Wikipedia In requirements engineering, a nonfunctional requirement is a requirement that specifies criteria that can be used to judge the operation of a system, rather than specific behaviours. This should be contrasted with functional requirements that define specific behaviours or functions. Software Development Method by Jan Pettersen Nytun, page 8

9 Requirements Analysis and Capture 2 Functional Requirements Functional requirements are often modeled with use cases. A use case is a short story describing a particular use of the system; a dialogue between an actor and the system. Visualized with a use case diagram and a descriptive text! Sometimes the user interface is developed or a prototype of the system is made. Software Development Method by Jan Pettersen Nytun, page 9

10 Requirements Analysis and Capture - 3 Nonfunctional Requirements From Wikipedia: Reliability, Security (observable at run time ) Testability, maintainability, extensibility and scalability (embodied in the static structure of the software system ) Software Development Method by Jan Pettersen Nytun, page 10

11 Requirements Analysis and Capture - 3 Nonfunctional Requirements Examples: From Wikipedia: A system may be required to present the user with a display of the number of records in a database. This is a functional requirement. How upto-date this number needs to be is a non-functional requirement. The data should be stored on ASCII files. Software Development Method by Jan Pettersen Nytun, page 11

12 Perspectives when it comes to diagrams - one possible way to classify this closer to the actual software solution Conceptual: The concepts of the problem domain are addressed. Analysis class diagrams PIMs. Specification: This perspective is typically employed under (early) design (PIM/PSM). Interfaces is typically specified, but not the implementation. Implementation: Class diagrams reflects the classes to implement PSMs. Software Development Method by Jan Pettersen Nytun, page 12

13 Requirements Analysis and Capture - 4 Domain Model High Level Conceptual Model When you make a domain model you capture/understand the key concepts of the problem domain. A domain model is typically visualized with class diagrams. Software Development Method by Jan Pettersen Nytun, page 13

14 Reality The Domain Domain Model Concepts From The Domain Person owner Car DESCRIBE AND UNDERSTAND THE MAIN CONCEPTS WITHIN THE DOMAIN It is a sort of thinking model Software Development Method by Jan Pettersen Nytun, page 14

15 Requirements Analysis and Capture - 5 Domain Model - A Simple OO Model The domain model is less detailed and precise than a design model, e.g., use only a subset of UML, it is not large. The same domain model may be used as basis for many applications - so keep the latest version Often there is a glossary of terms that describes the domain classes and other classes. It is important to have a common vocabulary! Software Development Method by Jan Pettersen Nytun, page 15

16 Design Deals with objects and functions that will be programmed. Some classes from the Domain Model may be used and extended with operations. Classes necessary for the implementation are added. The operations can be modeled with sequence diagrams showing responsibility and interaction. Software Development Method by Jan Pettersen Nytun, page 16

17 Design / Implementation Model The design ends up with an implementation model. Automatic or manual mapping to code. The implementation model is a full specification of the system. You can trace back from this model to the models on higher levels of abstraction. Software Development Method by Jan Pettersen Nytun, page 17

18 Relationships Between The Different Models - 1 The number of models and which abstraction levels to operation on is a matter of choice there is no completely right or wrong. The larger (complex) the system, the more time should be spent on modeling. Software Development Method by Jan Pettersen Nytun, page 18

19 Relationships Between The Different Models - 2 Generally (waterfall): You go from more abstract models and end up with implementation models. More and more details are added. You go from more logical models to more concrete ones. You go from PIMs to PSMs. You go from a user point of view to an implementation point of view. Software Development Method by Jan Pettersen Nytun, page 19

20 Models An Example Domain Model (conceptual model/pim): Concepts of the domain (real world classes) Analysis (requirement) Type Model (conceptual/specification model/pim): Software types that should be covered by the system Analysis / preliminary design Design Model (specification/pim/psm): Classes (with operations) that will be implemented Implementation Model (PSM): A fully specified system that can be mapped to code Software Development Method by Jan Pettersen Nytun, page 20

21 What is needed in the system Domain Model (an analysis model) Analysis/Type Model How should the system work Understand Design Model Refine Implementation Model Problem Domain Install Map to code Code / Implemented System Software Development Method by Jan Pettersen Nytun, page 21

22 Static path Requirements Analysis and Capture Use Cases use case 1 Domain Model class X attribut1... class X attribut1... method() Design Implementation Testing Design level Diagrams class Y attribut1... Coding class X{... }... Test Cases use case 1 use case 2 Use Case Texts <x>does<y>... Sequence Diagrams obj1 Obj2 met1() Methods void func1() {...}... use case 2 Functional path

23 Iterative Development [2] The waterfall method should only be used when the requirements are well understood and unlikely to change radically during system development. [1] As the developer work with a system and understand it better, the model must be iterated at all levels to capture that understanding; it is impossible to understand a large system in a single, linear pass. Software Development Method by Jan Pettersen Nytun, page 23

24 Iterative and incremental development. Each cycle consist of one or more of the process components (requirement, design,...), typically only a part (an increment) of the required functionality is implemented through each cycle. At each cycle the requirements are verified and validated, this can lead to changed requirements. In each cycle the most risky functionality is addressed, the cycle is aimed at eliminating the risk. In this way serious problems is exposed at an early stage, in some cases this can lead to termination of the project. Requirements / Analysis Design Implementation Testing Requirements... First Cycle... Software Development Method by Jan Pettersen Nytun, page 24

25 Types of risks The requirements do not specify the right system. The selected technology is not adequate for solving the given types of problems. People with the right skills are not available to the project. There are political forces that will try to stop or delay the project. Software Development Method by Jan Pettersen Nytun, page 25

26 High-level View Of The Development Phases (Unified Modeling Process) Inception - the vision of the project is received; initial ideas are discussed; a go-ahead of the project is given. Elaboration - the project is planned. Features and architecture is elaborated. Construction - the system is developed through a series of iterations. Transition - the product is set in production. User training is given. Analysis, design, are called modeling stages, these are not synchronized with the development phases. In each phase the cycle of requirement, design, implementation and testing is preformed repeatedly. Software Development Method by Jan Pettersen Nytun, page 26

27 The Development Process At each phase several complete cycles are possible. In the beginning requirements capture and analysis is focused, the other process components are more important later on. R/A = Requirements / Analysis D = Design I = Implementation T = Testing Example of development process: R/A R/A R/A D A D I D I T I T Inception Elaboration Construction Transition Software Development Method by Jan Pettersen Nytun, page 27

28 References [1] James Rumbaugh, Ivar Jacobson, Grady Booch: The Unified Modeling Language Reference Manual. Addison-Wesley, 1999 [2] Ian Sommerville: Software Engineering, Eight Edition. Addison-Wesley, 2007 Grady Booch, James Rumbaugh and Ivar Jacobson: The Unified Modeling Language User Guide. Addison-Wesley, 1999 James Rumbaugh, Michael Blaha, William Premerlani, Frederick Eddy and William Lorenzen: Object-Oriented Modeling and Design. Prentice Hall, 1991 Martin Fowler with Kendall Scott: UML Distilled. Addison-Wesley, 1997 Terry Quatrani: Visual Modeling with Rational Rose and UML. Addison-Wesley, 1998 Ari Jaaksi: A Method for Your First Object-Oriented Project. JOOP - The Journal of Object-Oriented Programming, Januar 1998 Rational software: Software Development Method by Jan Pettersen Nytun, page 28