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Chapter 9 Design Engineering

Chapter 9 Design Engineering. Flow-oriented elements. Data flow diagrams control flow diagrams Processing narratives. Analysis Model. Behavioral elements. component-level design. State diagrams Sequence diagrams. Scenario-based elements. i. n. t. e. r. f. a. c. e. d. e. s.

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Chapter 9 Design Engineering

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  1. Chapter 9Design Engineering

  2. Flow-oriented elements Data flow diagrams control flow diagrams Processing narratives Analysis Model Behavioral elements component-level design State diagrams Sequence diagrams Scenario-based elements i n t e r f a c e d e s i g n Use-cases (text) Use-case diagrams Activity diagrams Swim lane diagrams a r c h i t e c t u r a l d e s i g n data/class design Class-based elements DESIGN MODEL Class diagrams Analysis packages CRC models Collaboration diagrams 9.1 Design within the Context of SE 1/20

  3. 9.2 Design Process and Design Quality • the design must implement all of the explicit requirements contained in the analysis model, and it must accommodate all of the implicit requirements desired by the customer. • the design must be a readable, understandable guide for those who generate code and for those who test and subsequently support the software. • the design should provide a complete picture of the software, addressing the data, functional, and behavioral domains from an implementation perspective. • Three characteristics for a good design Please read Quality Guidelines in Section 9.2 2/20

  4. 9.2 Design Process and Design Quality • Design Principles (from Davis [DAV95] ) • The design process should not suffer from “tunnel vision”. • The design should be traceable to the analysis model. • The design should not reinvent the wheel. • The design should “minimize the intellectual distance” [DAV95] between the software and the problem as it exists in the real world. • The design should exhibit uniformity and integration. • The design should be structured to accommodate change. • The design should be structured to degrade gently, even when aberrant data, events, or operating conditions are encountered. • Design is not coding, coding is not design. • The design should be assessed for quality as it is being created, not after the fact. • The design should be reviewed to minimize conceptual (semantic) errors. 3/20

  5. door open manufacturer details of enter model number type algorithm swing direction inserts lights type number weight opening mechanism repeat until door opens turn knob clockwise; implemented with a "knowledge" of the if knob doesn't turn, then object that is associated with enter take key out; implemented as a data structure find correct key; insert in lock; endif pull/push door move out of way; end repeat 9.3 Design Concepts • Abstraction — data, procedure, control walk to door; reach for knob; open door; walk through; close door. • Refinement — top-down design strategy 4/20

  6. 9.3 Design Concepts • Architecture:The overall structure of the software and the ways in which that structure provides conceptual integrity for a system. [SHA95a] • Structural models: represent architecture as an organized collection of program components • Framework models: increase the level of abstraction by attempting to identify repeatable architectural design frameworks that are encountered in similar types of applications • Dynamic models: address the behavioral aspects of the program architecture, indicating how the structure or system configuration may change as a function of external events • Process models: focus on the design of the business or technical process that the system must accommodate. • Functional models: represent the functional hierarchy of the system 5/20

  7. 9.3 Design Concepts • Patterns Design Pattern Template • Pattern namedescribes the essence of the pattern • Intentdescribes the pattern and what it does • Also-known-assynonyms for the pattern • Motivationprovides an example of the problem • Applicabilityspecific design situations in which the pattern is applicable • Structureclasses that are required to implement the pattern • Participantsresponsibilities of the classes • Collaborationshow the participants collaborate to carry out their responsibilities • Consequencesdescribes the “design forces” that affect the pattern and the potential trade-offs • Related patternscross-references related design patterns 6/20

  8. module development cost cost of software module integration cost easier to build, easier to change, easier to fix ... optimal number number of modules of modules 9.3 Design Concepts • Modularity 发信人: liuyidaojian (山水涅磐), 信区: CS 标 题: 林锐的软件工程里的一段 发信站: 飘渺水云间 (Sun May 4 14:51:41 2003), 转信 模块就如同人的器官，具有特定的功能。人体中最出色的模块设计之一是手，手只有几种动作，却能做无限多的事情。人体中最糟糕的模块设计之一是嘴巴，嘴巴将最有价值但毫无相干的几种功能如吃饭、说话、亲吻混为一体，使之无法并行处理，真乃人类之不幸。 -- 昔我往 友 柳依依，今我来?，雨雪霏霏！ 人微言轻，以其不争，故天下莫与之争？ 树犹如此，人何以堪？ 万古长空，一朝风月！ ※ 来源:·飘渺水云间 Freecity.dhs.org·[FROM: liuyidaojian] 7/20

  9. module • algorithm controlled • data structure interface • details of external interface • resource allocation policy clients "secret" a specific design decision 9.3 Design Concepts • Information Hiding • reduces the likelihood of “side effects” • limits the global impact of local design decisions • emphasizes communication through controlled interfaces • discourages the use of global data • leads to encapsulation—an attribute of high quality design • results in higher quality software 8/20

  10. Great deal of dependence Independent  Highly coupled Loosely coupled Uncoupled  9.3 Design Concepts • Functional Independence • Coupling Goal: as loose as possible = as independent as possible 9/20

  11. 9.3 Design Concepts A: ……………… ……………… entry 1: ……………… ……………… entry 2: ……………… ……………… …… A B A: ………… ………… goto C1 ………… ………… C D C: ………… ………… C1: …… …… A B  Content Coupling: One module modifies another. The least desirable 10/20

  12. 9.3 Design Concepts Global : V1 V2 Global : V1 V2 A: ………… ………… A1=V1+V2 ………… ………… B: ………… ………… V1=B1 ………… ………… A: ………… ………… V1++ ………… ………… B: ………… ………… V2=B1+V1 ………… …………  Common coupling：Data are accessible from a common data store. 11/20

  13. 9.3 Design Concepts B Fn …… Flag A F2 …… Flag F1  Control coupling：One module passes parameters to control the activity of another module.  Data coupling ：Only data are passed. It is easy to trace data and make changes.  The most desirable. 12/20

  14. 9.3 Design Concepts from disk from tape from …… A: Read inputs • Cohesion: as cohesive as possible  Coincidental cohesion ：Unrelated functions, processes, or data are found in the same module (for convenience).  Logical cohesion：Logically related functions or data are placed in the same module.  Temporal cohesion：The functions are related only by the timing involved. 13/20

  15. 9.3 Design Concepts enter data check data manipulate data • Cohesion: (continued)  Procedural cohesion：Functions are grouped together in a module to ensure a certain order of performance.  Communicational cohesion：All the functions in a module operate on or produce the same data set.  Functional cohesion：Every processing element is essential to the performance of a single function. 14/20

  16. 9.3 Design Concepts Sizing Modules: Two Views 15/20

  17. 9.3 Design Concepts • Refactoring: change a software system in such a way that it does not alter the external behavior of the code [design] yet improves its internal structure. • When software is refactored, the existing design is examined for: • redundancy • unused design elements • inefficient or unnecessary algorithms • poorly constructed or inappropriate data structures • any other design failure that can be corrected to yield a better design. 16/20

  18. 9.3 Design Concepts • Design Classes • User interface classes • Business domain classes • Process classes – lower-level business abstractions required to fully manage the BD classes • Persistent classes – database • System classes – management and control functions 17/20

  19. high Analysis model Abstraction dimension c l R e q u i r e m e n t s : a s s d i a g r a m s a n a l y s i s p a c k a g e s c o n s t r a i n t s u s e - c a s e s - t e x t c l a s s d i a g r a m s C R C m o d e l s u s e - c a s e d i a g r a m s i n t e r o p e r a b i l i t y a n a l y s i s p a c k a g e s c o l l a b o r a t i o n d i a g r a m s a c t i v i t y d i a g r a m s C R C m o d e l s t a r g e t s a n d d a t a f l o w d i a g r a m s s w i m l a n e d i a g r a m s c o l l a b o r a t i o n d i a g r a m s c o n f i g u r a t i o n c o n t r o l - f l o w d i a g r a m s c o l l a b o r a t i o n d i a g r a m s d a t a f l o w d i a g r a m s p r o c e s s i n g n a r r a t i v e s s t a t e d i a g r a m s c o n t r o l - f l o w d i a g r a m s s e q u e n c e d i a g r a m s p r o c e s s i n g n a r r a t i v e s s t a t e d i a g r a m s s e q u e n c e d i a g r a m s d e s i g n c l a s s r e a l i z a t i o n s t e c h n i c a l i n t e r f a c e s u b s y s t e m s d e s i g n c o m p o n e n t d i a g r a m s c o l l a b o r a t i o n d i a g r a m s d e s i g n c l a s s r e a l i z a t i o n s N a v i g a t i o n d e s i g n d e s i g n c l a s s e s s u b s y s t e m s G U I d e s i g n a c t i v i t y d i a g r a m s c o l l a b o r a t i o n d i a g r a m s Design model d i a g r a m s s e q u e n c e d i a g r a m s c o d m e p s o i g n n e n c t l a s s e s a c t i v i t y d i a g r a m s s e q u e n c e d i a g r a m s r e f i n e m e n t s t o : r e f i n e m e n t s t o : c o m p o n e n t d i a g r a m s low d e s i g n c l a s s r e a l i z a t i o n s d e s i g n c l a s s e s s u b s y s t e m s a c t i v i t y d i a g r a m s c o l l a b o r a t i o n d i a g r a m s s e q u e n c e d i a g r a m s d e p l o y m e n t d i a g r a m s a r c h i t e c t u r e i n t e r f a c e c o m p o n e n t - l e v e l d e p l o y m e n t - l e v e l e l e m e n t s e l e m e n t s e l e m e n t s e l e m e n t s Process dimension 9.4 The Design Model 18/20

  20. abstraction 9.5 Pattern-based Software Design • Design patterns – a technique that reuses design elements that have proven successful in the past • A description of a design pattern may also consider a set of design forces. • Design forces describe non-functional requirements (e.g., ease of maintainability, portability) associated the software for which the pattern is to be applied. • Types of design patterns: • Architectural patterns • Design patterns (focus on a specific element of design) • Idioms (coding patterns) 19/20

  21. 9.5 Pattern-based Software Design • Framework – an architectural skeleton with a collection of “plug points” that enable it to be adapted to a specific problem domain. • Gamma et al note that: • Design patterns are more abstract than frameworks. • Design patterns are smaller architectural elements than frameworks • Design patterns are less specialized than frameworks 20/20

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