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Analysis and Design
Data Dictionary
As the name suggests the data dictionary is a catalog or repository of data
terms such as data elements, data structures etc. Data dictionary is a collection
of data to be captured and stored in the system, inputs to the systems and outputs
generated by the systems. So let's first know more about what are these data elements
and structures.
Data element
The smallest unit of data, which can not be further decomposed, is known as
a data element. For example any number digit or an alphabet will qualify to be
data elements. Data element is the data at the most fundamental level. These elements
are used to as building blocks for all other data in the system. At times data
elements are also referred as data item, elementary item or just as field. There
is a very little chance that only by them data element can convey some meaning.
Data structure
Data elements when clubbed together as a group make up a data structure. These
data elements are related to one another and together they stand for some meaning.
Data structures are used to define or describe the system's components.
Data dictionary entries consist of a set of details about the data used or
produced in the system such as data flows, data stores and processes. For each
item the dictionary records its name, description, alias and its length. The data
dictionary takes its shape during the data flow analysis and its contents are
used even till the system design. It very reasonable to know why the data dictionary
is so essential. There are numerous important reasons.
In a system there is data volume flow in the form of reports, documents etc.
In these transactions either the existing data is used or new data items are created.
This poses a potential problem for the analyst and thus developing and using a
well-documented dictionary can be a great help.
Now consider a case where everyone concerned with the system derives different
meanings for the same data items. This problem can continue until the meaning
of all data items and others are well documented so that everyone can refer to
the same source and derive the same common meaning.
Documentation in data dictionary is further carried on to record about the
circumstances of the various process of the system. A data dictionary is always
an added advantage for the system analysis. From the data dictionary one can determine
about the need of the new features or about the changes required. Thus they help
in evaluating the system and in locating the errors about the system description,
which takes place when the contents of the dictionary are themselves not up to
the mark.
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