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  Data Objects Attributes and Relationships

Introduction to Data Objects, Attributes and Relationships

When data modelling is used as a requirement  analysis technique the analysis begins by creating models  for  objects. A  data  objects can be  defined as:

It  is a representation  of  information that must  be understand by the software.

It  is defined  almost  in the same  manner as the  objects of the OOA. Data  objects can be  external entities  things  occurrences or  events  roles  organizational units, places or structures. It can  be better understood with  the help of an example:

A person busies a scoter.

Here person and scooter are the  data objects. So  the attributes  of each  one and a relationships  between both are defined. In this  way  they  are linked with  each other. This  example is shown in fig 7.30

As we can  see in fig 7.25, that each objects  has some  attributes  and they  are connected with each  other  via a link. These  relationships  are always defined  by the  context of the problem that is beings  analyzed.

A data  objects  encapsulate the  data so  there is so  reference within objects  to operations  that act  on the  data. That why are  objects can be  represented as a table 7.3.

In table 7.3, various  attributes of data objects scooter are defined.

In the table the attributes  of data  scooter are specifically  named and their  respective  entries are also  made. Id number is an  identifier model  and id  number represent the  naming  attributes. Body type  and color are descriptive  attributes  and the  own  of the scooter  is the  referential attributes ties  one data  objects to another.

So, this attributes makes the link between scooter  and the  person who buss it. The  body of the table 7.3 represents  specific instances of  the  data objects. For  example  model LA400, id number B23 of body type sports with color blue  and which is  bought by B, represents an instance of the data object scooter.

There are some major characteristics to define objects attributes. They are described below:

  • Name an instance of the data objects.
  • Describe the instance.
  • Make reference to another instance in another table

Additionally one or more of the  attributes  must  be defined  as an identifier where the  identifier attributes  becomes a key  attributes when we want  to find  an instance of the  data objects. The  values  of the  identifier must  be unique.  Attributes for data  objects are determined inexactly the same  way as suggested for attributes  defined as part of objects oriented  analysis.

To reduce the  redundancy and to provide consistency in table these data objects tables are formalized by applying a set of normalization  rules that will result in a relational model for the data. These normalization rules   are given  below:

1. A given  instance  of  a data  objects has one  and only one value for each objects.

2. Attributes represent  elementary data items  they  should contain no internal structure.

3. When more  than one attributes is used to identify  a data  objects  be sure that  descriptive  and referential attributes  represent  a characteristics of the  entire objects and not a characteristic of  some things that would be identified by only part of the  identifier.

All non identifier attributes  must  represent some  characteristic of the  instance named  by the  identifier  of the data  objects  and describe some  other  attributes that is not  an identifier.

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