SEC 308 Yazlm Mhendislii Software Design 1 Analysis

SEC 308 Yazılım Mühendisliği Software Design 1

Analysis Model -> Design Model 2

Design and Quality 0 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. 0 the design must be a readable, understandable guide for those who generate code and for those who test and subsequently support the software. 0 the design should provide a complete picture of the software, addressing the data, functional and behavioral domains from an implementation perspective. 3

Quality Guidelines 0 A design should exhibit an architecture that 0 (1) has been created using recognizable architectural styles or patterns, 0 (2) is composed of components that exhibit good design characteristics 0 (3) can be implemented in an evolutionary fashion 0 A design should be modular; that is, the software should be logically partitioned into elements or subsystems 0 A design should contain distinct representations of data, architecture, interfaces, and components. 0 A design should lead to components that exhibit independent functional characteristics. 0 A design should be represented using a notation that 4 effectively communicates its meaning.

Quality Attributes 0 Functionality: assess features & capabilities, generality of functions, security of overall system 0 Usability: assess human factors, consistency, and documentation 0 Performance: processing speed, response time, resource consumption… 0 Supportability: maintainability, compatibility, ease of configuration, ease of installation 5

Fundamental Design Concepts 0 abstraction—data, procedure, control 0 architecture—the overall structure of the software 0 patterns—”conveys the essence” of a proven design solution 0 modularity—compartmentalization of data and function 0 hiding—controlled interfaces 0 Functional independence—single-minded function and low coupling 0 refinement—elaboration of detail for all abstractions 0 Refactoring—a reorganization technique that simplifies the design 6

Data Abstraction door Manufacturer model number type swing direction inserts lights type number weight opening mechanism implemented as a data structure 7

Procedural Abstraction open details of enter algorithm implemented with a "knowledge" of the object that is associated with enter 8

Architecture “The overall structure of the software and the ways in which that structure provides conceptual integrity for a system. ” [SHA 95 a] 0 Structural properties. This aspect of the architectural design representation defines the components of a system (e. g. , modules, objects, filters) and the manner in which those components are packaged and interact with one another. For example, objects are packaged to encapsulate both data and the processing that manipulates the data and interact via the invocation of methods 0 Extra-functional properties. The architectural design description should address how the design architecture achieves requirements for performance, capacity, reliability, security, adaptability, and other system characteristics. 0 Families of related systems. The architectural design should draw upon repeatable patterns that are commonly encountered in the design of families of similar systems. In essence, the design should have the ability to reuse architectural building blocks. 9

Patterns 0 0 0 0 0 Design Pattern Template Pattern name—describes the essence of the pattern in a short but expressive name Intent—describes the pattern and what it does Also-known-as—lists any synonyms for the pattern Motivation—provides an example of the problem Applicability—notes specific design situations in which the pattern is applicable Structure—describes the classes that are required to implement the pattern Participants—describes the responsibilities of the classes that are required to implement the pattern Collaborations—describes how the participants collaborate to carry out their responsibilities Consequences—describes the “design forces” that affect the pattern and the potential trade -offs that must be considered when the pattern is implemented Related patterns—cross-references related design patterns 10

Modular Design 11

Modularity: Trade-offs What is the "right" number of modules for a specific software design? module development cost of software module integration cost optimal number of modules 12

Information Hiding module controlled interface • algorithm • data structure • details of external interface • resource allocation policy clients "secret" a specific design decision 13

Why Information Hiding? 0 reduces the likelihood of “side effects” 0 limits the global impact of local design decisions 0 emphasizes communication through controlled interfaces 0 discourages the use of global data 0 leads to encapsulation—an attribute of high quality design 0 results in higher quality software 14

Stepwise Refinement open walk to door; reach for knob; open door; walk through; close door. repeat until door opens turn knob clockwise; if knob doesn't turn, then take key out; find correct key; insert in lock; endif pull/push door move out of way; end repeat 15

Functional Independence 16

Sizing Modules: Two Views 17

Refactoring 0 Fowler [FOW 99] defines refactoring in the following manner: 0 "Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code [design] yet improves its internal structure. ” 0 When software is refactored, the existing design is examined for 0 redundancy 0 unused design elements 0 inefficient or unnecessary algorithms 0 poorly constructed or inappropriate data structures 0 or any other design failure that can be corrected to yield a better design. 18

The Design Model 19

Design Model Elements 0 Data elements 0 Data model --> data structures 0 Data model --> database architecture 0 Architectural elements 0 Application domain 0 Analysis classes, their relationships, collaborations and behaviors are transformed into design realizations 0 Patterns and “styles” (Chapter 10) 0 Interface elements 0 the user interface (UI) 0 external interfaces to other systems, devices, networks or other producers or consumers of information 0 internal interfaces between various design components. 0 Component elements 0 Deployment elements 20

Data Design 0 Data design translates data objects defined as part of the analysis model into 0 Data structures at the software component level 0 A possible database architecture at the application level 0 It focuses on the representation of data structures that are directly accessed by one or more software components 0 The challenge is to store and retrieve the data in such way that useful information can be extracted from the data environment 0 "Data quality is the difference between a data warehouse and a data garbage dump" 21

Software Architecture 0 The software architecture of a program or computing system is the structure or structures of the system which comprise 0 The software components 0 The externally visible properties of those components 0 The relationships among the components 0 Software architectural design represents the structure of the data and program components that are required to build a computer-based system 0 An architectural design model is transferable 0 It can be applied to the design of other systems 0 It represents a set of abstractions that enable software engineers to describe architecture in predictable ways 22

Example Software Architecture Diagrams 23

Why Architecture? 0 The architecture is not the operational software. Rather, it is a representation that enables a software engineer to: 0 (1) analyze the effectiveness of the design in meeting its stated requirements, 0 (2) consider architectural alternatives at a stage when making design changes is still relatively easy, and 0 (3) reduce the risks associated with the construction of the software. 24

Architectural Styles Each style describes a system category that encompasses: (1) a set of components (e. g. , a database, computational modules) that perform a function required by a system, (2) a set of connectors (subroutine call, remote procedure call, data stream, socket) that enable “communication, coordination and cooperation” among components, (3) semantic constraints that define how components can be integrated to form the system, and … • • • Data flow architectures Call and return architectures Data-centered architectures Virtual Machine architectures Independent Component architectures 25

A Taxonomy of Architectural Styles 26

Data Flow Architecture 27

Data Flow Architecture 0 Has the goal of modifiability 0 Characterized by viewing the system as a series of transformations on successive pieces of input data 0 Data enters the system and then flows through the components one at a time until they are assigned to output or a data store 0 Batch sequential style 0 The processing steps are independent components 0 Each step runs to completion before the next step begins 0 Pipe-and-filter style 0 0 Emphasizes the incremental transformation of data by successive components The filters incrementally transform the data (entering and exiting via streams) The filters use little contextual information and retain no state between instantiations The pipes are stateless and simply exist to move data between filters 0 Use this style when it makes sense to view your system as one that produces a well-defined easily identified output 0 The output should be a direct result of sequentially transforming a well-defined easily identified input in a time-independent fashion 28

Call and Return Architecture 29

Call and Return Architecture 0 Has the goal of modifiability and scalability 0 Has been the dominant architecture since the start of software development 0 Main program and subroutine style 0 Decomposes a program hierarchically into small pieces (i. e. , modules) 0 Typically has a single thread of control that travels through various components in the hierarchy 0 Remote procedure call style 0 Consists of main program and subroutine style of system that is decomposed into parts that are resident on computers connected via a network 0 Strives to increase performance by distributing the computations and taking advantage of multiple processors 0 Incurs a finite communication time between subroutine call and response 30

Call and Return Architecture 0 Object-oriented or abstract data type system 0 Emphasizes the bundling of data and how to manipulate and access data 0 Keeps the internal data representation hidden and allows access to the object only through provided operations 0 Permits inheritance and polymorphism 0 Layered system 0 Assigns components to layers in order to control inter-component interaction 0 Only allows a layer to communicate with its immediate neighbor 0 Assigns core functionality such as hardware interfacing or system kernel operations to the lowest layer 0 Builds each successive layer on its predecessor, hiding the lower layer and providing services for the upper layer 0 Is compromised by layer bridging that skips one or more layers to improve runtime performance 0 Use this style when the order of computation is fixed, when interfaces are specific, and when components can make no useful progress while awaiting the results of request to other components 31

Data-Centered Architecture 32

Data-Centered Architecture 0 Has the goal of integrating the data 0 Refers to systems in which the access and update of a widely accessed data store occur 0 A client runs on an independent thread of control 0 The shared data may be a passive repository or an active blackboard 0 A blackboard notifies subscriber clients when changes occur in data of interest 0 At its heart is a centralized data store that communicates with a number of clients 0 Clients are relatively independent of each other so they can be added, removed, or changed in functionality 0 The data store is independent of the clients 0 Use this style when a central issue is the storage, representation, management, and retrieval of a large amount of related persistent data 0 Note that this style becomes client/server if the clients are modeled as independent processes 33

Virtual Machine Architecture Program Data Program Instructions Interpretation Engine Program Internal State 34

Virtual Machine Architecture 0 Has the goal of portability 0 Software systems in this style simulate some functionality that is not native to the hardware and/or software on which it is implemented 0 Can simulate and test hardware platforms that have not yet been built 0 Can simulate "disaster modes" as in flight simulators or safety-critical systems that would be too complex, costly, or dangerous to test with the real system 0 Examples include interpreters, rule-based systems, and command language processors 0 Interpreters 0 Add flexibility through the ability to interrupt and query the program and introduce modifications at runtime 0 Incur a performance cost because of the additional computation involved in execution 0 Use this style when you have developed a program or some form of computation but have no make of machine to directly run it on 35

Independent Component Architecture Client A Client B Server Client D Client C Peer X Peer W Peer Y Peer Z 36

Independent Component Architecture 0 Consists of a number of independent processes that communicate through messages 0 Has the goal of modifiability by decoupling various portions of the computation 0 Sends data between processes but the processes do not directly control each other 0 Event systems style 0 Individual components announce data that they wish to share (publish) with their environment 0 The other components may register an interest in this class of data (subscribe) 0 Makes use of a message component that manages communication among the other components 0 Components publish information by sending it to the message manager 0 When the data appears, the subscriber is invoked and receives the data 0 Decouples component implementation from knowing the names and locations of other components 37

Independent Component Architecture 0 Communicating processes style 0 0 0 These are classic multi-processing systems Well-know subtypes are client/server and peer-to-peer The goal is to achieve scalability A server exists to provide data and/or services to one or more clients The client originates a call to the server which services the request 0 Use this style when 0 Your system has a graphical user interface 0 Your system runs on a multiprocessor platform 0 Your system can be structured as a set of loosely coupled components 0 Performance tuning by reallocating work among processes is important 0 Message passing is sufficient as an interaction mechanism among components 38

Architectural Design Steps 1) 2) 3) 4) Represent the system in context Define archetypes Refine the architecture into components Describe instantiations of the system 39

Architectural Context 0 Use an architectural context diagram (ACD) that shows 0 The identification and flow of all information into and out of a system 0 The specification of all interfaces 0 Any relevant support processing from/by other systems 0 An ACD models the manner in which software interacts with entities external to its boundaries 0 An ACD identifies systems that interoperate with the target system 0 Super-ordinate systems 0 Use target system as part of some higher level processing scheme 0 Sub-ordinate systems 0 Used by target system and provide necessary data or processing 0 Peer-level systems 0 Interact on a peer-to-peer basis with target system to produce or consume data 0 Actors 0 People or devices that interact with target system to produce or consume data 40

Architectural Context Diagram 41

Safe. Home ACD 42

Archetypes 0 Archetypes indicate the important abstractions within the problem domain (i. e. , they model information) 0 An archetype is a class or pattern that represents a core abstraction that is critical to the design of an architecture for the target system 0 It is also an abstraction from a class of programs with a common structure and includes class-specific design strategies and a collection of example program designs and implementations 0 Only a relatively small set of archetypes is required in order to design even relatively complex systems 0 The target system architecture is composed of these archetypes 0 They represent stable elements of the architecture 0 They may be instantiated in different ways based on the behavior of the system 0 They can be derived from the analysis class model 0 The archetypes and their relationships can be illustrated in a UML class 43 diagram

Example Archetypes in Humanity • • • • • Addict/Gambler Amateur Beggar Clown Companion Damsel in distress Destroyer Detective Don Juan Drunk Engineer Father Gossip Guide Healer Hero Judge King Knight Liberator/Rescuer • • • • • Lover/Devotee Martyr Mediator Mentor/Teacher Messiah/Savior Monk/Nun Mother Mystic/Hermit Networker Pioneer Poet Priest/Minister Prince Prostitute Queen Rebel/Pirate Saboteur Samaritan Scribe/Journalist • • • Seeker/Wanderer Servant/Slave Storyteller Student Trickster/Thief Vampire Victim Virgin Visionary/Prophet Warrior/Soldier (Source: http: //www. myss. com/Three. Archs. asp) 44

Example Archetypes in Software Architecture • • • Node Detector/Sensor Indicator Controller Manager • • Moment-Interval Role Description Party, Place or Thing (Source: Pressman) (Source: Archetypes, Color, and the Domain Neutral Compon 45

Archetypes – their attributes 46

Archetypes – their methods 47

Components 0 Based on the archetypes, the architectural designer refines the software architecture into components to illustrate the overall structure and architectural style of the system 0 These components are derived from various sources 0 The application domain provides application components, which are the domain classes in the analysis model that represent entities in the real world 0 The infrastructure domain provides design components (i. e. , design classes) that enable application components but have no business connection 0 Examples: memory management, communication, database, and task management 0 The interfaces in the ACD imply one or more specialized components that process the data that flow across the interface 0 A UML class diagram can represent the classes of the refined architecture and their relationships 48

Instantiations of the System 0 An actual instantiation of the architecture is developed by applying it to a specific problem 0 This demonstrates that the architectural structure, style and components are appropriate 0 A UML component diagram can be used to represent this instantiation 49

Component Structure 50

Refined Component Structure Instantiations of the System 51

Analyzing Architectural Design 0 Describe the architectural styles/patterns that have been chosen to address the scenarios and requirements: 0 module view 0 process view 0 data flow view 0 Evaluate quality attributes by considering each attribute in isolation. • • easier to test easier to maintain propagation of fewer side effects easier to extend 52

Deriving Program Architecture 53

Partitioning the Architecture • “horizontal” and “vertical” partitioning are required 54

Horizontal Partitioning • define separate branches of the module hierarchy for each major function • use control modules to coordinate communication between functions function 3 function 1 function 2 55

Vertical Partitioning: Factoring • design so that decision making and work are stratified • decision making modules should reside at the top of the architecture decision-makers workers 56

Why Partitioned Architecture? • • results in software that is easier to test leads to software that is easier to maintain results in propagation of fewer side effects results in software that is easier to extend 57

Structured Design • objective: to derive a program architecture that is partitioned • approach: – the DFD is mapped into a program architecture – the PSPEC and STD (state transition diagram) are used to indicate the content of each module • notation: structure chart 58

Flow Characteristics Transform flow: • Incoming flow • Transform center • Outgoing flow Transaction flow • A single data item 59

General Mapping Approach 0 isolate incoming and outgoing flow boundaries; for transaction flows, isolate the transaction center 0 working from the boundary outward, map DFD transforms into corresponding modules 0 add control modules as required 0 refine the resultant program structure using effective modularity concepts 60

Transform Mapping 61

Factoring 62

First Level Factoring main program controller input controller processing controller output controller 63

Second Level Mapping 64

Transaction Flow incoming flow action path T 65

Transaction Example Control panel display Display information Control panel Sensors commands Safe. Home Software Sensor status Alarm Type Alarm Telephone number tones Telephone Line 66

Transaction Mapping Principles 0 isolate the incoming flow path 0 define each of the action paths by looking for the "spokes of the wheel 0 assess the flow on each action path 0 define the dispatch and control structure 0 map each action path flow individually 67

Transaction Mapping Data flow model f e a d b mapping t x 1 program structure i g h l k m t b j a n d x 2 e x 4 x 3 f g l x 3. 1 h m n j i k 68

Isolate Flow Paths error msg command produce error msg read command validate command invalid command fixture setting status format setting read fixture status determine type robot control read record combined status record calculate output values send control value start/stop determine setting raw setting assembly record values format report 69

Map the Flow Model 70

Refining the Structure Chart 71

What is a Component? 0 OMG Unified Modeling Language Specification [OMG 01] defines a component as 0 “… a modular, deployable, and replaceable part of a system that encapsulates implementation and exposes a set of interfaces. ” 0 OO view: a component contains a set of collaborating classes 0 Conventional view: logic, the internal data structures that are required to implement the processing logic, and an interface that enables the component to be invoked and data to be passed to it. 72

OO Component What are the differences? Interface=method? OO view: a component contains a set of collaborating classes 73

Conventional Component n. Conventional view: n logic, the internal data structures that are required to implement the processing logic, and n an interface that enables the component to be invoked and data to be passed to it. 74

Cohesion and Coupling Cohesion 0 Conventional view: 0 the “single-mindedness” of a module 0 OO view: 0 a component or class encapsulates only attributes and operations that are closely related to one another Levels of cohesion 0 Functional, Layer, Communicational, Sequential, Procedural, Temporal, utility Coupling 0 Conventional view: 0 0 OO view: 0 0 The degree to which a component is connected to other components and to the external world a qualitative measure of the degree to which classes are connected to one another Level of coupling 0 Content, Common, Control, Stamp, Data, Routine call, Type use, Inclusion or import, 75 External

Component Level Design 0 Step 1. Identify all design classes that correspond to the problem domain, infrastructure domain. 0 0 0 Step 2. Elaborate all design classes (not acquired as reusable components). Step 2 a. Specify message details when classes or component collaborate. Step 2 b. Identify appropriate interfaces for each component. Step 2 c. Elaborate attributes and define data types and data structures. Step 2 d. Describe processing flow within each operation in detail. 0 Step 3. Describe persistent data sources (databases and files) and identify the classes required to manage them. 0 Step 4. Develop and elaborate behavioral representations for a class or component. 0 Step 5. Elaborate deployment diagrams to provide additional implementation detail. 0 Step 6. Factor every component-level design representation and always consider alternatives. 76

Activity Diagram What is this about wrt. Component-level design? What would be behavioral wrt. Component-level design? 77

Statechart What is this about wrt. Component-level design? How does this differ from AD wrt. Component-level design? 78

Collaboration Diagram What is this about wrt. Component-level design? 79

Refactoring 80

Algorithm Design 0 the closest design activity to coding 0 the approach: 0 review the design description for the component 0 use stepwise refinement to develop algorithm 0 use structured programming to implement procedural logic 0 use ‘formal methods’ to prove logic 81

Stepwise Refinement Recall: open walk to door; reach for knob; open door; repeat until door opens turn knob clockwise; walk through; if knob doesn't turn, then close door. take key out; find correct key; insert in lock; endif pull/push door move out of way; end repeat 82

Algorithm Design Model 0 represents the algorithm at a level of detail that can be reviewed for quality At which level? Component or Class? 0 options: 0 graphical (e. g. flowchart, box diagram) 0 pseudo code (e. g. , PDL). . . choice of many 0 programming language(? ) 0 decision table 0 conduct walkthrough to assess quality At which level? 83

Structured Programming for Procedural Design 0 uses a limited set of logical constructs: 0 Sequence “go-to” considered ? ? ? 0 Conditional — if-then-else, select-case 0 Loops — do-while, repeat until 0 leads to more readable, testable code 0 can be used in conjunction with ‘proof of correctness’ What’s more to Structured Programming than the above? 84

A Structured Procedural Design Can you add something to make this “unstructured? ? 85

Decision Tables: Another Ambiguity Test q Natural Language q“The system shall report to the operator all faults that originate in critical functions or that occur during execution of a critical sequence and for which there is no fault recovery response. ” (adapted from the specifications for the international space station) q A decision table originate in critical functions F T F T Occur during critical sequence F F T T No fault recovery response F F T T Report to operator? ? ? 86

Decision Table 87

Program Design Language (PDL) 88

Interface Design Easy to learn? Easy to use? Easy to understand? Typical Design Errors qlack of consistency qtoo much memorization qno guidance / help qno context sensitivity qpoor response q. Arcane/unfriendly Any examples? How about your remote controls? How about fighter airplanes? How are Windows OS and MS applications? How about UTD web sites? Vending machines? 89

Golden Rules • Place the user in control instead of ? • Reduce the user’s memory load dos vs. windows? • Make the interface consistent for the user …but, who’s the user? Should the user work with the designer, then, during UI design? 90

Place the User in Control 0 Define interaction modes in a way that does not force a user into unnecessary or undesired actions. 0 Allow user interaction to be interruptible and undoable. 0 Streamline interaction as skill levels advance and allow the interaction to be customized. linear text vs. pie chart? 0 Design for direct interaction with objects that appear on the screen. how? any examples? 91

Reduce the User’s Memory Load 0 Reduce demand on short-term memory. how many? 0 Establish meaningful defaults. 0 Define shortcuts that are intuitive. 0 The visual layout of the interface should be based on a real world metaphor. 0 Disclose information in a progressive fashion. 92

Make the Interface Consistent 0 Allow the user to put the current task into a meaningful context. 0 Maintain consistency across a family of applications. 0 If past interactive models have created user expectations, do not make changes unless there is a compelling reason to do so. 93

User Interface Design Process 94

Interface Analysis 0 Interface analysis means understanding 0 (1) the users who will interact with the system through the interface; 0 (2) the tasks that end-users must perform to do their work, 0 (3) the content that is presented as part of the interface 0 (4) the environment in which these tasks will be conducted 95

User Analysis 0 Are users trained professionals, technician, clerical, or manufacturing workers? 0 Are the users capable of learning from written materials or have they expressed a desire for classroom training? 0 Are users expert typists or keyboard phobic? 0 What is the age range, gender, primary spoken language of the user community? 0 Is the software to be an integral part of the work users do or will it be used only occasionally? 0 Are users experts in the subject matter that is addressed by the system? 96

Task Analysis and Modeling 0 Answers the following questions … 0 What work will the user perform in specific circumstances? 0 What tasks and subtasks will be performed as the user does the work? 0 What specific problem domain objects will the user manipulate as work is performed? 0 What is the sequence of work tasks—the workflow? 0 0 Use-cases define basic interaction Task elaboration refines interactive tasks Object elaboration identifies interface objects (classes) Workflow analysis defines how a work process is completed when several people (and roles) are involved 97

Swimlane Diagram What kind of diagram is this? What does this have to do with UI design? 98

Analysis of Display Content 0 Are different types of data assigned to consistent geographic locations on the screen (e. g. , photos always appear in the upper right hand corner)? 0 Can the user customize the screen location for content? 0 Will graphical output be scaled to fit within the bounds of the display device that is used? 0 How will color to be used to enhance understanding? 0 How will error messages and warning be presented to the user? 99