From one methodology to another, the strict definition of an attribute can have slight variations. However, in any methodology, an attribute is the component or element that contains a specific value or characteristic that describes an entity or object.
Class
A class is a description of a set of objects that share the same attributes, operations, methods, relationships, and semantics. A class can use a set of interfaces to specify collections of operations it provides to its environment.
Class attribute
In Object-Oriented modeling and design methodologies, class attributes contain data values that describe each object in a class. For example, the following list contains the attributes that describe the customer object:
•Name
•Age
•Address
•Telephone number
Each attribute contains a value that describes each object instance. This means that if you have 10 customers, you consider each one an instance. Consequently, each customer instance is described or differentiated by the attributes. Different object instances have specific values defined for each attribute; some are different than the attributes describing other instances, some are the same. However, each attribute name is unique in each class. Therefore, two different classes, the Customer class and the Supplier class, can each have the same attribute called address. In each one of those classes, the attribute name is unique.
Column
The column definition corresponds to a column in a database table. The following properties can be specified for a column:
•key status (PK component)
•nullity (null value allowed)
•uniqueness (candidate key)
•data type
•type qualifiers (length, precision)
•default value
•user data type (domain)
•extended attributes
•check constraints, database comments, and other DBMS specific column characteristics.
A column definition is specific to the table in which it is defined and is only related to other columns in other tables through foreign key constraints. This means that the only time two or more columns are related to one another is if they are foreign keys derived from the same origin, or one is the origin and the other a foreign key derived from it.
Data element
The data element definition specifies the characteristics that apply to all instances of the data, regardless of what model or entity it is used in:
•data type
•type qualifiers: length, precision
•default value
•check constraints
•data owner
•domain.
It is important to note that, since the physical characteristics belong to the data element, they are always inherited by all attributes used to represent the data.
Data structure
The term data structure refers to a scheme for organizing related pieces of information. The basic types of data structures include files, lists, arrays, records, trees, and tables.
Entity
An entity is some thing (customer, order, and so on) that the organization maintains information about. Relational database tables appear as entities in the data model; these are often referred to in technical texts as tables.
Table
A table is the basic unit of data storage in a database. It is the equivalent of a file.