Week 6

In week 5 we studied Traditional Approach to modell "things" & "events"
For Things in the system we use ERD to represent data entities and their relation i.e. what kind of information is needed and structure of the information.

For Event modelling we use many kind of diagrams;
1.CONTEXT DIAGRAM: we use Context Diagram as a abstract model to show the entire system as one process and to outline system boundaries and external entities.
2.DATA FLOW DIAGRAM:we use DFD diagrams to decomposite system into further level for clarification. Using number of DFD decomposition and number of processes in each decomposition level depends on system complexity but as a rule it's recommanded to have 7±2 process in each decomposition level.
N.B. what happens in DFD and within the process have to be described to avoid misunderstanding; we use 3 way to describe the processes: Structured English (psedue code), Decision Table & Decision Trees.
Likewise, we have to clarify our definition for data (entities in ERD), we list all the attributes of each entity with data description elements (their type and maximum values allowed e.g. String, or Boolean ) all these information will be placed in Data Dictionary.
other useful diagrams are; data dependency diagram which is for exploring activities about one single process, Location Diagram which is proccessing locaton of system, Activity Location Marix which describes what processes is performed in which place and Activity-data matrix which shows enetities & their privillages to change data. This can be described by CRUD i.e. Create-Read-Update-Delete.
3.Activity Diagram is another kind of diagram which illustrates the flow of control and procedures in the system. this diagram is also used in OOA as well.

Part 2: OOA Modelling
There are different kind of digrams in this approach but the underlying concept is the same. All the "Things" & "Events'' should be modelled.
We use Class Diagram for modelling "Thins" with concepts like Abstract class, attributes and methods for objects.
just a quick recap; in OOA we have OBJECTS and the main focus is on process rather than data itself. onbjects are main part of system and they are communicating by sending message and responding to messages.
class diagram includes objects that are represented by classes, attributes, behaviour (methods), and using concepts like inheritance and UML notaion for multiplexity.

Events are being modelled in OOA by:
1. USE CASE DIAGRAM: which is almost equivalant for context digram in traditional approach. they are being used to represent Actors i.e. someone or something external to system bundaries or automated system, and system itself which can include one or many use case. Use-case diagram can be seen as equivalant to DFD in diferrent level when they represent subsystems.
Like we described the process of DFD, we have to describe the use-case here. this is achieved by developing USE CASE DETAILED DESCRIPTION which can be develop at three level; brief, intermediate and Fully developed description.
2. ACTIVITY DIAGRAM: as mentioned before this kind of diagram is used in both approaches to represent the procedure and order of use cases.
3. SYSTEM SEQUENCE DIAGRAM (SSD): is used to represent interaction between objects i.e. what is the detaill of message sent to an object and what the object returns in the response messsage.
4. STATE MACHINE DIAGRAM: is another diagram which is helpful for describing business rules