HP System Dictionary/XL General Reference Manual Vol 1 (32256-90004)

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1 Introduction
Overview
This chapter provides a brief description of System Dictionary/XL and the operating environment required
for the product. It also provides information about the programming languages and subsystems that
System Dictionary supports.
Data Dictionaries
Just as an ordinary dictionary is a collection of definitions of words, a data dictionary is a collection of
definitions and descriptions of data that resides on a computer system. In a dictionary, the smallest unit of
information is a word, while in a data dictionary the smallest unit of information is a data element.
You can compare a data dictionary to the file card system in a public library. Each card in the file contains
a description of a book in the library, and lists the title, author, publisher, location in the library, etc. of the
book. The card itself is not the book, but only represents and describes it.
Like the file cards, a data dictionary does not contain the data itself, but contains metadata --data about
data. This metadata can be descriptions and definitions of various kinds. It can describe such things as:
Data: Names and definitions of data elements
Data Relationships: How data is related to other data
Data Responsibility: Who is responsible for what data
Organizational Structure: The information flow, who uses the data
Location Information: Where files, programs, and reports reside
Security Information: Who has access to what data
A typical example of a piece of metadata is a data element called "SSN", which represents a piece of data--
a social security number. The social security number itself does not reside in the dictionary, but a
description of that piece of data does. For instance, the data dictionary might tell you the name of the data
element, the storage length, the display or output length, the type of data (numeric or character), its sign if
the element is numeric, which database or program that data resides in, and possibly which departments
in the organization use and maintain that data.
The data dictionary, therefore, serves many purposes. You can use it as a quick directory to the
information that resides on a computer system--where to go to get pieces of data. You can also, however,
use it as one of the primary means for ensuring consistency of data definitions and preventing data
redundancy. This means that programmers and developers may be required to check the data dictionary
for data elements that already exist on their system before they design a new program.
Therefore, if a data element already exists on the system describing a social security number (for example,
"SSN"), the dictionary reports this information and does not allow the programmer to add a new element
with the same name. This helps an organization to save time in program development by using data
definitions that already exist. It also saves data storage space by preventing data redundancy and helps to
standardize data definitions within an organization.
For a more detailed introduction to what data dictionaries are and how an organization can use a data
dictionary, see the HP primer entitled Managing Your Information Network: A Data Dictionary Primer.