1. 10/12/2001Data Structure1 Relationships Between The Data Flow Diagram and The Systems Design Activities Mohammad A. Rob School of Business and Public Administration University of Houston-Clear Lake Houston, Texas 77058

2. 10/12/2001Data Structure2 Introduction Data-flow diagramming technique (DFD) is used to understand the business processes of a system.

3. 10/12/2001Data Structure3 Relationships Between The Data Flow Diagram and The Systems Design Activities The data flow diagrams also contain information on the four essential components of a systems, namely –the input –output –program modules –data storage Processes Inputs Data Outputs

4. 10/12/2001Data Structure4 We modify the system concept such that its components are within the dotted-line boundary and the external entities (of DFD) interact with the system through the input and output components.

5. 10/12/2001Data Structure5 Relationships Between The Data Flow Diagram and The Systems Design Activities The goal of a systems analyst is to extract necessary information on the input, program modules, data storage, and output components of a system from the data flow diagrams and then design these components.

6. 10/12/2001Data Structure6 Relationships Between The Data Flow Diagram and The Systems Design Activities Data Dictionary First, a data dictionary is created that describes all data flows, data stores, processes, and external entities of the data-flow diagrams. The data-flows and data stores are then expanded to describe the data structure associated with each of these components. Each data structure is further expanded to describe the data elements that comprise the data structure.

7. 10/12/2001Data Structure7 Relationships Between The Data Flow Diagram and The Systems Design Activities Data Storage Design Once the data-structures associated with all data stores in the data flow diagrams are defined, they are organized to understand the relationships between the data elements of various data stores. Files and databases that comprise the data storage component of a system, are designed on the basis of these data stores.

8. 10/12/2001Data Structure8 Relationships Between The Data Flow Diagram and The Systems Design Activities Data Storage Design Entity-relationship diagrams are commonly used for data modeling or database design. The data stores in the data-flow diagram become the entities in the entity-relationship diagram. Entity Data Store

9. 10/12/2001Data Structure9 Relationships Between The Data Flow Diagram and The Systems Design Activities Input Design The data flows originated from the external entities and ending to the processes in a data flow diagram carry information on the input components of a system. The data structures associated with the input data flows are described in the data dictionary. These data structures are used to design the data-entry forms or screens of a system.

10. 10/12/2001Data Structure10 Relationships Between The Data Flow Diagram and The Systems Design Activities Output Design The data flows originated from the processes and ending to the external entities in a data flow diagram carry information on the output components of a system. The data structures associated with the output data flows are described in the data dictionary. These data structures are used to design the output reports or statements of a system.

11. 10/12/2001Data Structure11 Relationships Between The Data Flow Diagram and The Systems Design Activities Program Modules Design The business processes in the data flow diagrams become the program modules of a system. Structure chartsStructure charts are commonly used to illustrate the relationships between the program modules of a system The levels of a structure chart typically correspond to the levels of a data flow diagramThe levels of a structure chart typically correspond to the levels of a data flow diagram Main Sub Context-level 0-level

12. 10/12/2001Data Structure12 Relationships Between The Data Flow Diagram and The Systems Design Activities It should be clear that the data dictionary of a system is solely based on the data flow diagram, but the design activities are based on both the “data flow diagrams” and the “data dictionary” Understanding this relationship is not obvious when the individual design activities and their associated tools are presented as independent activity

13. 10/12/2001Data Structure13 Relationships Between The Data Flow Diagram and The Systems Design Activities

14. 10/12/2001Data Structure14 Illustration of the Relationship Between The DFD and Data Dictionary The data dictionary of a system requires three stages of descriptions: –Describe all components of the data flow diagrams –Describe the data structures associated with the data flow and data store –Describe data elements associated with the data structure

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16. 10/12/2001Data Structure16 Illustration of the Relationship Between The DFD and Data Dictionary

17. 10/12/2001Data Structure17 Illustration of the Relationships Between The DFD and The Systems Components There are many components in a data flow diagram. All these components collectively participate in the design activities of the system components But only a set of these data flow diagram components are used to design an individual component of a system.

18. 10/12/2001Data Structure18 Illustration of the Relationships Between The DFD and The Systems Components In order to clarify the relationship between the DFD and the system components, we rearrange the data flow diagram components to fit into the system model.

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20. 10/12/2001Data Structure20 Illustration of the Relationships Between The DFD and The Systems Components We move all data store components of the DFD and enclose within the boundary of the data storage component of a system. All external entities of the DFD are enclosed in two external entities of the system. The rest of the DFD components, which include all the processes and the data flows are enclosed in a boundary of program modules component of a system.

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22. 10/12/2001Data Structure22 Illustration of the Relationships Between The DFD and The Systems Components With the illustration, the knowledge of the design activities becomes simple. All data stores in the data flow diagram participate in the data storage design – for files and/or database. All data flows originating from the external entities and leading towards the program modules are considered for the input design.

23. 10/12/2001Data Structure23 Illustration of the Relationships Between The DFD and The Systems Components Similarly, all data flows originating from the program modules and leading to the external entities are considered for the design of the output components. All the processes and data flows enclosed by the outer boundary of the program modules are considered for program design.