Mumbai University > Computer Engineering > Sem 5 > SOOAD

Marks: 10M

Year: May 2015

1. System modeling:

• System modeling helps the analyst to understand the functionality System modeling helps the analyst to understand the functionality of the y of the system and models are used to communicate with customers

• Different models present the system from different perspectives

  • External perspective showing the system’s context or environment context or environment
  • Behavioral perspective showing the behavior of the system
  • Structural perspective showing the system or data architecture
• Model types
  • Data processing model Data processing model showing how the data is processed at different stages
  • Composition model Composition model showing how entities are composed of other entities
  • Architectural model Architectural model showing principal sub-systems
  • Classification model Classification model showing how entities have common characteristics
  • Stimulus/response model Stimulus/response model showing the system’s reaction to events

1. Context models
2. Context models are used to illust Context models are used to illustrate the operational context of rate the operational context of a system a system they show what lies outside the system boundaries. They show what lies outside the system boundaries.
3. Social and organizational concerns may affect the decision on where to Position system boundaries. Position system boundaries.
4. Architectural models show the system and its relationship with other Systems.

1. Process models:
2. Process models show the overall Process models and the processes that are supported by the system.
3. Data flow models may be used to show the processes and the flow show the processes and the flow of information from one process to another.

1. Data-processing models
2. Data flow diagrams (DFDs) may be used to model the system’s data Processing.
3. These show the processing steps as data flows through a system.
   • DFDs are an intrinsic part of many analysis methods.
   • Simple and intuitive notation that customers can understand.
   • Show end-to-end processing of data.
   • DFDs model the system from a functional perspective.

1. State machine models
2. These model the behavior of the system in response to external and Internal events.
3. They show the system’s responses to stimuli so are often used for modeling real time systems.
4. State machine models show system states as nodes and events as arcs Between these nodes. When an event occurs, the system moves from one state to another.
5. Statecharts
   • An integral part of the UML and are used to represent state machine models.
   • 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.

1. Semantic data models
2. Used to describe the logical structure of data processed by the system.
3. An entity-relation-attribute model sets out the entities in the system, the relationships between these entities and the entity attributes.
4. Widely used in database design. Can readily be implemented using relational databases.
5. No specific notation provided in the UML but objects and associations can be used.

1. Object models
2. Object models describe the system in terms of object classes and their associations.
3. An object class is an abstraction over a set of objects with common attributes and the services (operations) provided by each object.
4. Various object models may be produced
   • Inheritance models;
   • Aggregation models;
   • Interaction models.
5. Natural ways of reflecting the real Natural ways entities manipulated by the world system.
6. More abstract entities are more difficult to model using this approach.
7. Object class identification is recognized as a difficult process requiring a requiring a deep understanding of the application domain.

8. Object classes reflecting domain entities are reusable across systems.

9. Inheritance models:

10. Organize the domain object classes into a hierarchy.
11. Classes at the top of the hierarchy reflect the common features all classes.
12. Object classes inherit their attributes and services from one more super-classes. These may then be specialized as necessary

13. Class hierarchy design can be a difficult process if duplication in different branches is to be avoided.

14. Object models and the UML:

15. The UML is a standard representative devised by the developers of widely used object oriented analysis and design methods.
16. It has become an effective standard for object-oriented modeling.

1. Multiple inheritance:
2. Rather than inheriting the attributes and services from a single parent class, a system which supports multiple inheritance allows object classes to inherit from several super-classes.
3. This can lead to semantic conflicts where attributes/services with the same name in different super-classes have different semantics.
4. Multiple inheritance makes class hierarchy reorganization more complex.

1. Object aggregation:
2. An aggregation model shows how classes that are collections are Composed of other classes.
3. Aggregation models are similar to the part Aggregation relationship in semantic data models.

1. Object behavior modeling:
2. A behavioral model shows the interactions between objects to produce some particular system behavior that is specified as a use-case.
3. Sequence diagrams (or collaboration diagrams) in the UML are used to model interaction between objects.