Objectives: Introduction Over View of System Analysis and Design
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- 6.4.2.2 Describing Data Structures
| 6.4.2.1 Describing Data Elements The description of a data element should include the name, description and an alias (synonym. For example AUTHOR NAME first WHISKEY – name - middle - distiller - last - vintage - alias The description should be a summary of the data element. It may include an example. We may also want to include whether or not the data elements(s) has 1. A different name. For example a PURCHASE ORDER may exist as PUR.ORDER, PUCHASE ORD., or PO. We want to record all these in the data dictionary and include them under the PUCHASE ORDER definition and separately with entires of their own. One example is PO. alias of (or see also) PUCHASE ORDER Then we lookup PUCHASE ORDER to find the details. It is an index. 2. Usage characteristics, such as a range of values or the frequency of use or both. A value is a code that represents a meaning. Here we have two types of data elements a. Those that take a value within a range for example, a payroll check amount between $ and $10,000 is called continuous value. b. Those that have a specific value for example. Departments in a firm maybe coded 100 (accounting, 110 (personnel, etc. Ina data dictionary, it is described as follows 100 means Accounting Department 101 means “ Accounts Receivable Section 102 means “ Accounts Payable Section 108 means “ General Ledger Section 3. Control information such as the source, date of origin, users, or access authorizations. 4. Physical location in terms of a record, file or database. 6.4.2.2 Describing Data Structures We describe any data structure by specifying the name of each data structure and the elements it represents, provided they are defined elsewhere in the data dictionary. Some elements are mandatory, whereas others are optional. To illustrate, let us take BOOK- DETAILS. The data elements of this data structure areas follows |