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

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Presentation on theme: "Chapters 7 & 9 System Scope DFDs, Use Cases, ERDs."— Presentation transcript:

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

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

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

4 Process Modeling l 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) l Utilize information gathered during requirements determination l Processes and retained data are modeled

5 Data Flow Diagram (DFD) l A picture of the movement of data between external entities and the processes and data stores within a system l 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.) l Process: work or actions performed on data (inside the system) l Data store: data at rest (inside the system) l Source/sink: external entity that is origin or destination of data (outside the system) l 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 l 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 l Alternative to DFDs (especially Level-0)

11 UML Use Case Diagram Symbols Use Case Actor Boundary Connection Include relationship Extend relationship >

12 What is an Actor? l Actor is an external entity that interacts with the system. l Most actors represent user roles, but actors can also be external systems. l 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? l A boundary is the dividing line between the system and its environment. l Use cases are within the boundary. l Actors are outside of the boundary.

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

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

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

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

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

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22 Gathering Information for Conceptual Data Modeling l 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 l What are subjects/objects of the business?  Data entities and descriptions l What unique characteristics distinguish between subjects/objects of the same type?  Primary keys l What characteristics describe each subject/object?  Attributes and secondary keys l How do you use the data?  Security controls and user access privileges

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

25 Summary l 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


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