© 2000 Franz Kurfess System Design Methods 1 CSC 205: Software Engineering I Dr. Franz J. Kurfess Computer Science Department Cal Poly

© 2000 Franz Kurfess System Design Methods 2 Course Overview u Introduction u Requirements Engineering u Requirements Elicitation u Requirements Management u Project Management u System Design Methods and Notations u Design Models and Object- Oriented Design u Design Analysis and Formal Specification u Design Analysis and Verification u Conclusions

© 2000 Franz Kurfess System Design Methods 3 Chapter Overview System Design Methods and Notations u Motivation u Objectives  Context Models  Behavioral Models  Data Models  Object Models  CASE workbenches u Important Concepts and Terms u Chapter Summary

© 2000 Franz Kurfess System Design Methods 4 Logistics u Midterm u Friday, February 16 u Project Presentations u probably Friday, Feb. 9 u with Lori Fisher

© 2000 Franz Kurfess System Design Methods 5 Bridge-In

© 2000 Franz Kurfess System Design Methods 6 Pre-Test

© 2000 Franz Kurfess System Design Methods 7 Motivation  it is helpful to consider a system from different perspectives in order to get a better understanding  various methods concentrate on specific aspects  components  functions  data flow  data structures  tools affiliated with these methods help with the capturing of system information

© 2000 Franz Kurfess System Design Methods 8 Objectives  to explain why the context of a system should be modeled as part of the re process  to describe behavioral modeling, data modeling and object modeling  to introduce some of the notations used in the Unified Modeling Language (UML)  to show how CASE workbenches support system modeling [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 9 Evaluation Criteria

© 2000 Franz Kurfess System Design Methods 10 [Sommerville 01] System Models  abstract descriptions of systems whose requirements are being analyzed

© 2000 Franz Kurfess System Design Methods 11 System Modeling  helps the analyst to understand the functionality of the system  models can be used to communicate with customers  different models present the system from different perspectives  external perspective  the system’s context or environment  behavioral perspective  the behavior of the system  structural perspective  the system or data architecture [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 12 Structured Methods  incorporate system modeling as an inherent part of the method  these methods define  a set of models  a process for deriving these models and rules  guidelines that should apply to the models  CASE tools support system modeling as part of a structured method [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 13 Structured Method Weaknesses  do not model non-functional system requirements  do not usually include information about whether a method is appropriate for a given problem  may produce too much documentation  the system models are sometimes too detailed and difficult for users to understand [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 14 [Sommerville 01] Model Types  data processing model  how the data is processed at different stages  composition model  how entities are composed of other entities  architectural model  principal sub-systems  classification model  entities with common characteristics  stimulus/response model  the system’s reaction to external or internal events

© 2000 Franz Kurfess System Design Methods 15 Context Models  used to illustrate the boundaries of a system  social and organizational concerns may affect the decision on where to position system boundaries  architectural models  show the system and its relationship with other systems [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 16 ATM System Context [Sommerville 01] Automated Teller Security System Account Data Base Usage Data Base Maintenance System Branch Counter System Branch Accounting System

© 2000 Franz Kurfess System Design Methods 17 Process Models  show the overall process and the processes that are supported by the system  data flow models  may be used to show the processes and the flow of information from one process to another [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 18 Equipment Procurement Process [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 19 Behavioral Models  behavioral models are used to describe the overall behavior of a system  two types of behavioral model are shown here  data processing models  show how data is processed as it moves through the system  state machine models  show how the system responds to events  both of these models are required for a description of the system’s behavior [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 20 Data-processing Models  data flow diagrams  used to model the system’s data processing  show the processing steps as data flows through a system  intrinsic part of many analysis methods  simple and intuitive notation that customers can understand  show end-to-end processing of data [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 21 Order Processing DFD [Sommerville 01] slightly different notation from examples in the previous chapter [FJK]

© 2000 Franz Kurfess System Design Methods 22 Data Flow Diagrams  DFDs model the system from a functional perspective  tracking and documenting how the data associated with a process is helpful to develop an overall understanding of the system  data flow diagrams may also be used in showing the data exchange between a system and other systems in its environment [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 23 CASE Toolset DFD [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 24 State Machine Models  model the behavior of the system  in response to external and internal events  show the system’s responses to stimuli  often used for modeling real-time systems  notation  system states as nodes  events as arcs between these nodes  when an event occurs, the system moves from one state to another  state charts are an integral part of the UML [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 25 Microwave Oven Model [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 26 Microwave Oven State Description [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 27 Microwave Oven Stimuli [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 28 State Charts  allow the decomposition of a model into sub-models  a brief description of the actions is included  following the ‘do’ in each state  can be complemented by tables describing the states and the stimuli [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 29 Microwave Oven Operation [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 30 Semantic Data Models  describe the logical structure of data processed by the system  entity-relation-attribute model  entities in the system  relationships between these entities  entity attributes  widely used in database design  can readily be implemented using relational databases  no specific notation provided in the UML  objects and associations can be used [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 31 Software Design Semantic Model [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 32 Data Dictionaries  lists of all of the names used in the system models  also includes descriptions of the entities, relationships and attributes  advantages  support name management and avoid duplication  store of organizational knowledge linking analysis, design and implementation  many CASE workbenches support data dictionaries [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 33 Data Dictionary Entries [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 34 Object Models  describe the system in terms of object classes  an object class is an abstraction over a set of objects  common attributes  services (operations) provided by each object  various object models may be produced  inheritance models  aggregation models  interaction models [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 35 Object Models  natural ways of reflecting the real-world entities manipulated by the system  more abstract entities are more difficult to model  object class identification is a difficult process  requires a deep understanding of the application domain  object classes reflecting domain entities may be reusable across systems [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 36 Inheritance Models  organize the domain object classes into a hierarchy  classes at the top of the hierarchy reflect the common features of all classes  object classes inherit their attributes and services from one or more super-classes  may then be specialized as necessary  class hierarchy design is a difficult process  duplication in different branches should be avoided [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 37 The Unified Modeling Language  devised by the developers of widely used object- oriented analysis and design methods  the “three amigos” Booch, Jacobson, Rumbaugh  has become an effective standard for object-oriented modeling  can be used at different levels of abstraction  conceptual level  specification level  implementation level [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 38 UML Models  functional model  use case diagrams  object model  class diagram  objects, attributes, associations, operations  dynamic model  sequence diagrams  state chart diagrams  activity diagrams

© 2000 Franz Kurfess System Design Methods 39 UML Notation  object classes  rectangles with the name at the top, attributes in the middle section and operations in the bottom section  associations  relationships between object classes  shown as lines linking objects  inheritance  is referred to as generalization  shown ‘upwards’ rather than ‘downwards’ in a hierarchy

Library Class Hierarchy [Sommerville 01]

User Class Hierarchy

© 2000 Franz Kurfess System Design Methods 42 Multiple Inheritance  allows object classes to inherit from several super- classes  rather than inheriting the attributes and services from a single parent class  can lead to semantic conflicts  attributes/services with the same name in different super- classes have different semantics  can simplify specifications of objects substantially  may make class hierarchy reorganization more complex [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 43 Multiple Inheritance [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 44 Object Aggregation  aggregation model  shows how classes which are collections are composed of other classes  similar to the part-of relationship in semantic data models [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 45 Object Aggregation [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 46 Object Behavior Modeling  behavioral model  shows the interactions between objects to produce some particular system behavior that is specified as a use-case  sequence diagrams (or collaboration diagrams) in the UML are used to model interaction between objects [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 47 Issue of Electronic Items [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 48 CASE Workbenches  coherent set of tools designed to support related software process activities  such as analysis, design or testing  analysis and design workbenches  support system modeling during both requirements engineering and system design  these workbenches may support a specific design method or may provide support for a creating several different types of system model [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 49 An Analysis and Design Workbench [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 50 Analysis Workbench Components  diagram editors  model analysis and checking tools  repository and associated query language  data dictionary  report definition and generation tools  forms definition tools  import/export translators  code generation tools [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 51 Post-Test

© 2000 Franz Kurfess System Design Methods 52 Evaluation u Criteria

© 2000 Franz Kurfess System Design Methods 53 Important Concepts and Terms  inheritance model  interaction model  multiple inheritance  object  object class  object model  process model  requirements  sequence diagram  stimulus-response model  state chart/diagram  state machine model  system model  Unified Modeling Language (UML)  use case diagram  activity diagram  aggregation model  architectural model  association  behavioral model  CASE workbench  classification model  component  composition model  context model  data dictionary  data flow  data flow diagram  data model  data structure  entity-relation-attribute model  entity-relationship diagram

© 2000 Franz Kurfess System Design Methods 54 Chapter Summary

© 2000 Franz Kurfess System Design Methods 55 Chapter Summary  a model is an abstract system view  complementary types of model provide different system information  context models show the position of a system in its environment  together with other systems and processes  data flow models may be used to model the data processing in a system  state machine models describe the system’s behavior  in response to internal or external events [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 56 Chapter Summary (cont.)  semantic data models describe the logical structure of data items  object models describe the logical system entities and their classification and aggregation  CASE workbenches support the development of system models [Sommerville 01]

© 2000 Franz Kurfess System Design Methods 57