semantic data model in DBMS pdf

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 Semantic Data Model in DBMS pdf:

Semantic Object Model introduction:

The semantic object model is a logical representation of data in an organization. It views the entire computer network system as a collection of objects related to one another. The semantic object model takes semantic objects as the basic element. It is based on the concepts presented by Codd engineer. It was first presented in 1988. The semantic object model can represent the perceptions of the users more closely than the E-R model.

Semantic Objects:

computer-system

A semantic object is a thing that can be identified in the user's working environment. Semantic means "meaning". Semantic objects are used to represent or model the meaning of the user's data. 
Semantic objects are grouped into classes. Each object has a unique name. For example, different classes in a university are STUDENT, Teacher, and DEPARTMENT, etc.
A particular semantic object is known as an instance of the STUDENT class, "Abdullah" is an instance of a TEACHER class, and "Computer Science" is an instance of the DEPARTMENT class.

For example:

Different classes in a university are students, teachers, and departments, etc.

Attributes:

An object has many attributes in DBMS. Each attribute represents the characteristics of the object. For example, an object of the STUDENT class can have attributes like Name, Address, Email, and Phone, etc. These attributes are used to describe the object. When we define objects for a database system, we use only those attributes, which are important for the system. The remaining attributes are ignored. For example, weight is an attribute of a student but it is normally not used in a college database because it is not important. 

Types of Attributes:

Simple Attributes:

It is the attribute that contains a single value, Roll no, Marks and Salary are examples of simple attributes.

Group Attributes:

Group attributes are composites of other attributes. For example, Name is a collection of FirstName and LzastName, Address is a collection of Street, Town, City, and Country.

Semantic Object Attribute:

They are the attributes the establish relationships between one semantic object to another semantic object.
The object is indicated by rectangles. The name of the object appears on the top of the rectangle and the attributes are written after the name of the object in the rectangle.
  1. Attribute Cardinality
  2. Object Class & Object Instances
  3. Object Identifiers

Attributes Domain:

A collection of possible values of an attribute is said to be an attribute domain. The domain of a simple attribute in a semantic object consists of two types of descriptions:
  • Physical Description
  • Semantic Description
The physical description indicates the type of data. For example, the Name of a student would be a string value, and Roll no should exceed 99, etc.
The Semantic description indicates the function or purpose of the attribute in it. For example, the Name of a student should be valid. This is a semantic description of the Name attribute of the student. This restriction is related to the meaning of the attribute. For example, "Math" is not a valid name even if it consists of string value because it does not satisfy the semantic description of the Name attribute.

Semantic Object Views:

database-coding

A part of an object that is displayed in a particular application is said to be as a view or semantic object view. One object can be displayed in different views as required in a semantic. Suppose we want to generate two reports i.e. one for displaying all students in a college and one for displaying all students in a college and one for displaying all professors in a college. These reports are two different views of COLLEGE. Some attributes of COLLEGE will be displayed in both views such as Name and Address.

Types of Objects:

Types of objects use some new terms, which are as follows:

  • Single-Valued Attribute:

It is an attribute whose maximum cardinality is 1.

  • Multi-Valued Attributes:

It is an attribute whose maximum cardinality is greater than 1.

  • Non-object Attribute:

It is a simple or group attribute

Types of Objects:

  • Simple Objects:
A simple object is a semantic object that contains only single-valued, non-object attributes. For example, this object contains only simple attributes. So this object is called a simple object
  • Composite Objects
A composite object is a semantic object that contains one or more multi-valued, non-object attributes. For example, the following figure shows a composite object BILL. This object contains multi-valued attributes services. A customer may get one or more services so this is called a composite object.
  • Compound Objects 
A compound object is a semantic object that contains at least one object attribute which we use in it. For example, the following figure shows a composite object BILL.this object contains multi-valued attribute services. a customer may get one or more services.so this is called a composite object.
  • Hybrid Objects
A hybrid object is a semantic object that is a combination of two object types. for example, if an object contains the properties of both composite and compound types, it will be called a hybrid object. The following figure shows a hybrid object ROOMobject attribute and rent attribute.so this is called a hybrid object.
  • Association Objects
An association object is a semantic object that connects two or more objects and stores data about that relationship. The following example shows three objects PILOTS, AIRPLANE, and FLIGHT. The FLIGHT object is used as an association object and stores data about the association of PILOT and AIRPLANE. 
  • Parent/Subtype Objects
A subtype object is a semantic object that inherits the attributes of an existing object. The inherited object is called the parent object. Suppose we have an object PERSON with different attributes such as Name, Address, and Phone, etc. If we want to create another object STUDENT, we can inherit the attributes of the PERSON object in the STUDENT object. Because the STUDENT is also a PERSON and has the same attributes as a PERSON object like Name, Address, and Phone.
  • Archetype/Version Objects
An archetype object is a semantic object that produces other objects to represent versions, releases, or editions of the archetype object. Suppose we have a semantic object BOOK with some attributes. We can create another semantic object to represent different editions of the book of the semantic objects.






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