Data Models:

Data models comprise a set of conceptual tools that describe data. These models are mainly used to specify the overall logical structure of a database and to provide a higher-level description of the implementation. Data models fall into three different categories - record-based logical models, object-based logical models, and physical data models. Figure 8.6 shows the evolution of these data models and their structures.

Record-Based Logical Models (RBLMs):

RBLMs are used for describing data at the logical and view levels. The logical level describes the type of data stored in the database and their interrelationships while the view level allows the users to see a set of application programs that hide the details of the data types (discussed later). These models are so named because the database is structured into numerous types of records that are of fixed format, i.e., each record type defines a fixed number of fields or attributes and each field is usually of a fixed length.

RBLMs are used both to specify the overall logical structure of the database and to provide a higher level description of the implementation. The relational, network, and hierarchical models fall under RBLM.

Relational model

In a relational model, data in several files is related through the use of a common key field. Each record in the file has the same key field but unique key field contents. The field can thus be used to identify a record. The computer uses this key field as an index to locate records without having to read all the records in the files.

In the relational model, a two-dimensional table is generally used for representing data and relationships. Each row corresponds to a record, while each column corresponds to a field. Unique keys or primary keys are used to access records in a table.
A relational database structure can link a customer file and an accounts receivable file by using a common field, such as the customer account number field. The user can then request a report consisting of fields from both the customer and the accounts receivable records. As a relational DBMS can work with many files and relate all the data, many databases focusing on different themes can be created.

Network model

The network model is the oldest DBMS model. The first network model was developed by GE[1] in the mid-1960s and was called the Integrated Data Store (IDS). Data in the network model is represented by a collection of records and the relationships among data are represented by pointers or links. Pointers store the location or address of files and records. The records in the database are organized as collections of arbitrary graphs.

Network databases support many-to-many relationships. They may be suitable for handling voluminous transactions but not for handling ad hoc requests. The relational model provides ad hoc request flexibility.

Hierarchical model

The hierarchical model is quite similar to the network model. It differs from the network model in the sense that the records are organized as a collection of trees rather than as arbitrary graphs. Also, the records are not represented by pointers but on the basis of the values that they have.

The hierarchical model is designed to handle large transaction-based applications like sales-order processing, check processing, inventory updating, patient billing, insurance file maintenance, etc. These applications are large, have well-defined master file of information and have a large number of well-structured transactions that are repeatedly processed.

Object-Based Logical Models (OBLMs):

OBLMs allow the user to specify data constraints explicitly. They are also used for describing data at the logical and the view levels. However, they differ from RBLMs as they provide flexibility in structuring and allow data constraints to be explicitly specified.

The entity-relationship (E-R) model and the object-oriented model fall under OBLM (discussed later). Other models include the binary model, semantic data model, infological model, and the functional data model.

Physical Data Models:

Physical data models are used to describe data at the physical or the lowest level, i.e., in the form of bytes and words. These data models are basically used for designing the internal schema of a database. Schema (discussed later) is a term used to describe the overall design of a database. The physical data models are also used for identifying tables, columns, relationships, data normalization, etc. The unifying model and frame memory model come under the physical data models.

Email based Information technology and system assignment help - homework help at Expertsmind

Are you searching Computer science expert for help with Data Models questions?  Data Models topic is not easier to learn without external help? We at www.expertsmind.com offer finest service of Information technolgy and system assignment help and Information technology homework help. Live tutors are available for 24x7 hours helping students in their Data Models related problems. We provide step by step Data Models question's answers with 100% plagiarism free content. We prepare quality content and notes for Data Models topic under Information technology theory and study material. These are avail for subscribed users and they can get advantages anytime.

Why Expertsmind for assignment help

1. Higher degree holder and experienced experts network
2. Punctuality and responsibility of work
3. Quality solution with 100% plagiarism free answers
4. Time on Delivery
5. Privacy of information and details
6. Excellence in solving Information Technolgoy and system queries in excels and word format.
7. Best tutoring assistance 24x7 hours