1. Chapters 7 & 9 System Scope
DFDs, Use Cases, ERDs

2. Agenda Summary Documenting System Scope Context and Level-0 DFDs
Use Case Diagrams
Enterprise Entity-Relationship Diagrams
Summary

3. Scope What’s in and what’s out: boundary Constraints and givens
What can change
Who / what is affected

4. Process Modeling
Graphically represent the processes that capture, manipulate, store, and distribute data between a system (what’s in) and its environment (what’s out) and among system components (functionalities)
Utilize information gathered during requirements determination
Processes and retained data are modeled

5. Data Flow Diagram (DFD)
A picture of the movement of data between external entities and the processes and data stores within a system
Difference from system flowcharts:
DFDs depict logical data flow independent of technology
Flowcharts depict details of physical systems

6. DFD Symbols

7. DFD Symbols (cont.)
Process: work or actions performed on data (inside the system)
Data store: data at rest (inside the system)
Source/sink: external entity that is origin or destination of data (outside the system)
Data flow: arrows depicting movement of data

8. Context Diagram
Context diagram shows the system boundaries, external entities that interact with the system, and major information flows between entities and the system.
NOTE: only one process symbol, and no data stores shown.

9. Level-0 DFD
Level-0 DFD shows the system’s major processes, data flows, and data stores at a high level of abstraction.
Processes are labeled 1.0, 2.0, etc. These will be decomposed into more primitive (lower-level) DFDs.

10. Use Cases
Depiction of a system’s behavior or functionality under various conditions as the system responds to requests from users
What are tasks in which each actor (external entity) is involved
Alternative to DFDs (especially Level-0)

11. UML Use Case Diagram Symbols
Actor
Boundary
Connection
Include relationship
Extend relationship
<<include>>
<<extend>>

12. What is an Actor?
Actor is an external entity that interacts with the system.
Most actors represent user roles, but actors can also be external systems.
An actor is a role, not a specific user; one user may play many roles, and an actor may represent many users.

13. What is a Boundary?
A boundary is the dividing line between the system and its environment.
Use cases are within the boundary.
Actors are outside of the boundary.

14. What is a Connection?
A connection is an association between an actor and a use case.
Depicts a usage relationship
Connection does not indicate data flow

15. What is an <<extend>> Relationship?
A connection between two use cases
Extends a use case by adding new behavior or actions
Specialized use case extends the general use case

17. What is an <<include>> Relationship?
A connection between two use cases
Indicates a use case that is used (invoked) by another use case
Links to general purpose functions, used by many other use cases

19. Conceptual Data Modeling
A detailed model that captures the overall structure of data in an organization
Independent of any database management system (DBMS) or other implementation considerations
Enterprise data model: the major categories of data and the relationships between the categories

20. Process of Conceptual Data Modeling
Develop a data model for the current system
Develop a new conceptual data model that includes all requirements of the new system
In the design stage, the conceptual data model is translated into a physical design
Project repository links all design and data modeling steps performed during SDLC

22. Gathering Information for Conceptual Data Modeling
Two perspectives
Top-down
Data model is derived from an intimate understanding of the business.
Bottom-up
Data model is derived by reviewing specifications and business documents.

23. Requirements Determination Questions for Data Modeling
What are subjects/objects of the business?
Data entities and descriptions
What unique characteristics distinguish between subjects/objects of the same type?
Primary keys
What characteristics describe each subject/object?
Attributes and secondary keys
How do you use the data?
Security controls and user access privileges

24. Requirements Determination Questions for Data Modeling (cont.)
Over what period of time are you interested in the data?
Cardinality and time dimensions
Are all instances of each object the same?
Supertypes, subtypes, and aggregations
What events occur that imply associations between objects?
Relationships and cardinalities
Are there special circumstances that affect the way events are handled?
Integrity rules, cardinalities, time dimensions

25. Summary Scope: What may change (in vs. out)
What interactions must be preserved
What are major functionalities
Who / what will be affected
Processes, data, people, systems