1. Data Dictionary What does “Backordered item” mean? What does “New Customer info.” contain? How does the “account receivable report” look like?

2. Data Dictionary A list of names used in the system models arranged alphabetically and their meaning and information about them Types of information provided: –Description of data –If composite data, describe elements –Data representation or type –Creator, creation date, user contacts –Other names for the data (aliases)

3. Data Dictionary Data dictionary is a metadata Created in parallel with DFD Created in top-down approach Data dictionary should be kept up-to-date with the DFD model

4. Data Dictionary Advantages: –Documentation for the whole system –Eliminate redundancy in a system which has been created by different people –Identify aliases –Provide a starting point to develop reports and screens –Validates the data flow diagrams for completeness and accuracy –Develop the logic for DFD processes

5. Data flow Description ID number Name (as it appears in DFD) Description Source Destination Type (file, screen, report, form, internal) Data structure name How frequently produced Comments

6. Data Store ID number Name Alias name Description Type (manual, computerized) File format (database, sequential, Indexed) Maximum/ average number of recording File name Data structure

7. Data Structure For compositional data flow and data store elements Describe the elements of the data structure using algebraic notation =Composed of { }Repetition ( )Optional + and [ / ] or

8. Data Structure Example: Student record= student ID + Student name+ Address + Date of birth + Gender + Nationality + Telephone number + (mobile telephone number) + { course record} Course record= course name + Course number+ Grade

9. Data Elements Each element in the data structure should be described –ID number –Name –Alias –Description –Type (Base: entered from user, derived: computed) –Length (in characters) [max or fixed] –Data type (date, numeric, alphanumeric) –Input/Output format –Validation criteria –Default value –Comments

10. Process Data Process number Process name Description Input Output Type (batch, online, manual) Prewritten code: ready made functional libraries Process logic Reference to description tables or structures Unresolved issues: notes to check with users

11. Describing Processes Using structured English or pseudo code Advantages –Understand how the process works and go back to users if not clear –Describe what should happen for designer and programmer –Validate the DFD

12. Describing Processes Example: Bonus monthly payment (Structured English) For each customer Read Customer record For each item rented between 1/10 to 1/11 add total End for If total is greater than or equal to 50$ then send bonus and thank you letter End if End for

13. Logical and Physical data Logical data structures is what the user sees Physical data structure is what the software needs for processing –(e.g. flags, key fields for search,..)

14. Automatic Data Dictionary Using CASE tools: –Easy to change and add –Created and integrated with other models –Checks that the DFD is valid e.g. all data needed for a process is input to it Data store contains data input/ output to/from it Derived data should be output from process Checks data source and destination in DFD –Use data structures to create reports and screens