OBJECT-BASED LOGICAL MODELS

Object-Relational Database(ORD)

An Object-Relational Database (ORD) or Object-Relational Database Management System (ORDBMS) provides a relational database management system that allows developers to integrate a database with their own custom data-types and methods. The term object-relational database sometimes also refers to external software products running over traditional DBMS to provide similar features - systems more correctly described as object-relational mapping systems.

Whereas traditional RDBMS or SQL-DBMS products focused on the efficient management of data drawn from a limited set of data-types (defined by the relevant language standards), an object-relational DBMS allows software-developers to integrate their own types and the methods that apply to them into the DBMS.

ORDBMS-technology aims to allow developers to raise the level of abstraction at which they view the problem domain.

OBJECT-BASED LOGICAL MODELS

Entity-Relationship Model

The (E-R) data model is based on a perception of a real worker that consists of a collection of basic objects, called entities, and of relationships among these objects.

The entity-relationship model for data uses three features to describe data. They are;

1. Entities, which specify distinct real-world items in an application.

2. Relationships, which connect entities and represent meaningful dependencies between them.

3. Attributes, which specify properties of entities and relationships.

Record-Based Logical Models

Relational Model

The relational model was introduced in an academic paper by E.F.Codd in 1970 as a way to make database management systems more independent of any particular application.

The relational database model is based upon the conception of implementing the database with the mathematical set theory. In this model, data is collection of tables called Relation in the set theory. The tabular representation of data contains rows and columns in which rows represent set of attributes of individual entity and columns represent the attribute of entity.

Three key terms are used extensively in relational database models; relations, attributes, and domains. A relation is a table with columns and rows. The named columns of the relation are called attributes, and the domain is the set of values the attributes are allowed to take.

All relations in a relational database have to adhere to some basic rules to qualify as relations. First, the ordering of columns is immaterial in a table. Second, there can't be identical tuples or rows in a table. And third, each tuple will contain a single value for each of its attributes.

Components of the Relational Model

1. Collections of objects or relations that store the data.

2. A set of operators that can act on the relations to produce other relations.

3. Data integrity for accuracy and consistency.

RECORD-BASED LOGICAL MODELS

 Network Model

Network model was developed with the view to eliminate the problems faced by hierarchical database during 1980s. The network model (defined by the CODASYL specification) organises data using two fundamental constructs, called records and sets. Records contain fields (which may be organised hierarchically, as in the programming language COBOL). Sets define one-to-many relationships between records: one owner, many members. A record may be an owner in any number of sets, and a member in any number of sets.

A network database model is a database model that allows multiple records to be linked to the same owner file. The model can be seen as an upside down tree where the branches are the member information linked to the owner, which is the bottom of the tree. The multiple linkages which this information allows the network database model to be very flexible. In addition, the relationship that the information has in the network database model is defined as many-to-many relationship because one owner file can be linked to many member files and vice versa.

                                                                                                                                                                           Network Model

Advantages of Network Database

Network database offer many advantages other than ones offered by hierarchical database. Some of them are mentioned below:

1. Simplicity: Similar to the hierarchical model, this model is simple and the implementation is effortless.

2. Ability to Manage More Relationship Types: The network model has the ability to manage one-to-one (1:1) as well as many-to-many (N: N) relationships.

3. Flexibility in data access: Data items can be navigated in more than one way providing the much desired flexibility of the data access.

4. Data Integrity: In a network model, there's always a connection between the parent and the child segments because it depends on the parent-child relationship.

5. Data Independence: Data independence is better in network models as opposed to the hierarchical models.

6. Standards: Universal standards have been developed and enforced in these types of databases.

Disadvantages of Network Database

Although network databases displayed significant improvement over hierarchical databases yet they suffered from disadvantages as mentioned:

1. Functional Flaws: Because a great number of pointers is essential, insertion, updates, and deletion become more complex.

2. Lack of Structural Independence: A change in structure demands a change in the application as well, which leads to lack of structural independence.

3. System Complexity: Each and every record has to be maintained with the help of pointers, which makes the database structure more complex.