After successive levels of data flow diagrams are complete, systems analysts use them to help catalog the data processes, flows, stores, structures, and elements in a data dictionary. Of particular importance are the names used to characterize data items. When given an opportunity to name components of data-oriented systems, the systems analyst needs to work at making the name meaningful but exclusive of other existing data component names.This chapter covers the data dictionary, which is another method to aid in the analysis of data-oriented systems.
Using a top-down approach, the systems analyst uses data flow diagrams to begin compiling a data dictionary, which is a reference work containing data about data, or metadata, on all data processes, stores, flows, structures, and logical and physical elements in the system being studied. One way to begin is by including all data items from data flow diagrams.
A larger collection of project information is called a repository. CASE tools permit the analyst to create a repository that may include information about data flows, stores, record structures, and elements; about procedural logic screen and report design; and about data relationships. A repository can also contain information about project requirements and final system deliverables; and about project management information.
Each entry in the data dictionary contains the item name, an English description, aliases, related data elements, the range, the length, encoding, and necessary editing information. The data dictionary is useful in all phases of analysis, design, and ultimately documentation, because it is the authoritative source on how a data element is used and defined by users in the system. Many large systems feature computerized data dictionaries that cross-reference all programs in the database using a particular data element. The data dictionary can also be used to create XML that enables businesses with different systems, software, or database management systems to exchange data.
Once you have mastered the material in this chapter you will be able to:
- Understand how analysts use data dictionaries for analyzing data-oriented systems.
- Create data dictionary entries for data processes, stores, flows, structures, and logical and physical elements of the systems being studied, based on DFDs.
- Understand the concept of a repository for analysts’ project information and the role of CASE tools in creating them.
- Recognize the functions of data dictionaries in helping users update and maintain information systems.