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Data Dictionary


The data dictionary is a textual list of all concepts that are defined during the analysis. The purpose of the data dictionary is to define a vocabulary that is common to all the members of the development team and to the customers and users of the system.

It is important to notice that the data dictionary is not a separate list of entities that is unrelated to the other models in the requirements analysis. Rather it can be seen as a different viewpoint on the same set of basic concepts that are used and defined in the use cases and in the requirements object model. For example all domain objects should be added to the data dictionary as soon as they are defined in the object model.

For each entity defined in the data dictionary at least the name of the entity and a brief explanation of the entity must be supplied.

Note that although the data dictionary is created in the requirements analysis it can be used during the entire development process and be updated when new concepts are found also in the other activities. The following Example 646 shows a part of a data dictionary for the access control system.

Example 646 : A part of a data dictionary description

NOUNS

Access control system - A system to control the 
access rights to an office. Unauthorized persons 
should not be able to enter without permission.

Card - Each employee working in the office has a 
card and a corresponding personal code. 

Card reader - The hardware into which the employee 
enters the card. The cardreader reads the cardId.

Code - Each employee has a four digit personal code 
connected to the card. To enter the office the 
employee must type the code on the keypad.

Display - The hardware unit by which the system 
tells the employee what to do.

Door - Employees enter and exit the office by 
opening a door.  The door is always kept locked and 
unlocks only when the employee enters the office 
with a valid card and code or when the employee is 
leaving the office by pressing the exit button. Each 
door provides a cardreader, keypad and display on 
the outside of the office and an exit button on the 
inside.

Keypad - The hardware unit used to type personal 
codes.  The keypad has keys for the digits 0-9.

Employee - The holder of a position in the office. 
Every employee has a registered card with a personal 
code to get access to the office.


RELATION PHRASES

Card with code - Each employee in the office has a 
card with a a personal code.

Code consists of four digits - The personal code 
that every employee has got, consists of four 
digits.

Door provides local panel - Each door has a 
localpanel on the outside of the office.  This 
localpanel is made up of a card reader, a display 
and a keypad.

Door provides exit button - Each door has an exit 
button on the inside of the office.

Registerfile contains employee identifications, 
cardnumbers and codes - The registerfile contains 
the data relevant to the access control system.


VERB PHRASES

Connection is lost - The connection between a door 
and the central controller can sometimes fail.  In 
case of broken connection nobody can enter the 
office.  It is, however, possible to leave the 
office.

Inform employee - The system gives the employee 
instructions by means of the display.

Enter office - A use case which describes the 
interaction between an employee and the access 
control system when the employee wants to enter the 
office.

Exit office - A use case which describes the 
interaction between an employee and the access 
control system when the employee wants to exit the 
office.
Validate card - The central controller validates a 
card with respect to info in the registerfile.

Validate code - The central controller validates the 
correctness of a code with respect to info in the 
registerfile.

In Example 646, the items in data dictionary are categorized into nouns, relation phrases and verb phrases. By categorizing the items, it may be easier to find the objects, attributes, operators, actors and use cases and also the relations between these entities in each model.


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