Data Dictionary : its development and use.

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Data Dictionary : its development and use

WHAT IS DATA DICTIONARY

Data dictionary is a catalogue of all data used in an application, their names, type and their origin. In other words it is data about data which is called metadata. Data dictionary gives a single point reference of data repository of an organization. It is thus an important documentation which would be useful to maintain a system

HOW IS DATA DICTIONARY DEVELOPED?

The Starting point of developing a data dictionary is a DFD.

Example:

Consider the Receiving office DFD.

image

WORD STATEMENT OF REQUIREMENTS FOR THE ABOVE DFD

• Vendor sends items with a delivery note while fulfilling an order (along with the physical items) to a receiving office.

• Receiving office compares a delivery note against order placed. If there is a discrepancy a discrepancy note is sent to purchase office.

• Actual items received note is sent to the inspection office along with items received.

DATA ELEMENTS IN DATA FLOW

From word statement we derive data elements in each data flow.

•Order no,Vendor name,Vendor address,item name,delivery date,quantity supplied,units Item name and Vendor name may not be unique. To ensure uniqueness we assign unique codes for them. Name of item is however still kept as it is to aid people.

Thus delivery note is:

Delivery note = Order no + Vendor code + Vendor name + Vendor address + item code + item name + delivery date + quantity supplied + units.

Discrepancy note : Order no + Vendor code + Vendor name + Vendor address + item code + item name + delivery date + quantity supplied + units + excess/deficiency + no of days late/early.

Items received note = Delivery note

Data in data store

Order records = order no + vendor code + vendor name + vendor address + item code + item name + order date + qty ordered + units + delivery period.

TYPICAL CHARACTERSTICS OF DATA ELEMENTS(CONTD)

Data dictionary gives in detail the characteristics of a data element. Typical characteristics are:

Data name : Should be descriptive and self explanatory.This will help in documentation and maintenance

Data description : What it represents

Origin : Where the data originates e.g. input from forms, comes from receiving office, keyed in by user etc.

Destination : Where data will flow and will be used (if any)

Data Type : numeric, alphanumeric,letters(or text),binary(0 or 1; True or False), Integer, Decimal fixed point, real(floating point), currency unit, date

Length : no of columns needed Limits on value : (if relevant)

e.g. upper and lower bounds of value (age>0,<100)

Remarks : (if any)

EXAMPLE OF DATA DICTIONARY ENTRY

1)

Name : Order number

Description : Used to identify order given to vendor

Origin : Part of delivery note from vendor

Destination : Receiving process

Data type : Numeric Integer

Length : 8 digits

Limits on value : >000,<=99999999

Actual value not relevant.Used only as unique identifier

Remarks: It is a key field.

2)

Name : Delivery date

Description : Date item is to be delivered

Origin : Part of delivery note from vendor.Is also in orders data store which is input to receiving process

Destination : Receiving process

Data type : Numeric Integer

Length : 8 digits

Limits on value : Date field in the form DDMMYYYY. Should satisfy constraints of a date in calendar

Remarks: Blank fields not allowed. e.g.05082004 is ok but not 582004

DATA DICTIONARY USES

Data dictionary can be enormous in size. Requires careful development. However, it is centralized reference document. It is an invaluable resource to design input forms, screens, data checking programs, process specification and database. It is very useful in understanding and maintaining system

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