Data Model:

A model is an abstraction procedure that hides superfluous details. Data modelling is utilized for representing entities of interest and their relationship in the database.

Data model as well as different types of Data Model.

Data model is a collection of concepts that are able to be used to describe the structure of a database which provides the necessary signifies to achieve the abstraction. The structure of a database signifies that holds the data.

•    data types
•    relationships
•    constraints

Types of Data Models:

1) High Level- Conceptual data model
2) Relational or Representational
3) Low Level- Physical data model
4) Object-Relational Models
5) Object-oriented Data Models

The most general data models are:

1. High Level-conceptual data model:

User level data model is the high level or else conceptual model. This offers concepts that are close to the way that many users perceive data.

2. Low level-Physical data model:

Provides concepts that explain the details of how data is stored in the computer model. Low level data model is merely for Computer specialists not for end-user.

3. Representation data model:

It is among High level & Low level data model which provides concepts that may be understood by end-user but that aren’t too far removed from the way data is organized by within the computer.

4) Relational Model:

The Relational Model utilizes a collection of tables both data as well as the relationship among those data. Every table have multiple columns and each column has a unique name.

Relational database including of two tables:

Customer –Table:

Account –Table:

Customer Preethi and Rocky share the similar account number A-111

Advantages:

a) The major advantage of this model is its ability to represent data in a simplified format.
b) The process of manipulating record is making simpler with the use of certain key attributes used to retrieve data.
c) Representation of different kinds of relationship is possible with this model.

5) Network Model:

The data in the network model are symbolized by collection of records and relationships among data are represented by links, which can be viewed as pointers.

The records in the database are prepared as collection of arbitrary groups.

Advantages:

a) Representation of relationship among entities is implemented using pointers which allows the representation of arbitrary relationship

b) Distinct the hierarchical model it is easy.

c) Data manipulation is able to be done easily with this model.

6) Hierarchical Model:

A hierarchical data model is a data model that the data is organized into a tree like structure. The structure permits repeating information using parent/child relationships: Every parent can have many children but each child only has one parent. All attributes of a precise record are listed under an entity type.

Advantages:

a) The representation of records is completed using an ordered tree which is natural method of implementation of one–to-many relationships.

b) Proper ordering of the tree results in easier as well as faster retrieval of records.

c) Permits the use of virtual records. This result in a steady database especially when modification of the data base is made.

7) Object-oriented Data Models:

a) Numerous models have been proposed for implementing in a database system.

b) One set includes models of persistent O-O Programming Languages such as C++ (example in OBJECTSTORE or VERSANT), and Smalltalk (example in GEMSTONE).

c) In addition systems like O2 ORION (at MCC – then ITASCA) IRIS (at H.P. - utilized in Open OODB).

8) Objects-Relational Models:

a) Most Recent Trend is started with Informix

b) Universal Server

c) Relational systems comprises concepts from object databases leading to object relational

d) Object Database Standard- ODMG-93, ODMG-version 2.0 and ODMG-version 3.0

e) Demonstrate in the newest versions of Oracle-10i, DB2 and SQL Server and other DBMSs

f) Standards incorporated in SQL-99 and expected to be enhanced in future SQL standards

Schemas versus Instances:

Database Schema:

The explanation of a database.

Comprises descriptions of the data types, database structure and the constraints on the database

Schema Diagram:

An illustrative display of (most aspects of) a database schema.

Schema Construct:

A component of the schema or else an object within the schema example STUDENT, COURSE

Database State:

The real data stored in a database at a particular moment in time. This comprises the collection of all the data in the database. As well called database instance (or occurrence or snapshot).

The term instance is as well applied to individual database components example record table instance, instance and entity instance

Database Schema vs. Database State:

Database State:

It refers to the content of database at a moment in time.

Initial Database State:

It refers to the database state when it is primarily loaded into the system.

Valid State:

A state that persuade the structure and constraints of the database.

Distinction:

The database schema changes much infrequently.

The database state changes each time the database is updated

• Schema is as well called intension
• State is as well called extension

DBMS Languages:

• DDL (Data Definition Language)
• DML (Data Manipulation Language)
• High-Level or else Non-procedural Languages- These comprise the relational language SQL
• May be utilized in a standalone way or may be embedded in a programming language
• Low Level or else Procedural Languages:

These should be embedded in a programming language.

Data Definition Language (DDL):

Used by the DBA and database designers to state the conceptual schema of a database.

a) In many DBMSs the DDL is as well used to define internal and external schemas (views).

b) In some DBMSs detach storage definition language (SDL) and view definition languages (VDL) are used to define internal and external schemas.

c) SDL is usually realized via DBMS commands provided to the DBA and database designers

Data Manipulation Language (DML):

Used to specify database retrievals as well as updates DML commands (data sublanguage) can be embedded in a general-purpose programming language (host language) such as C, C++, COBOL or Java.

a) A library of functions can as well be provided to access the DBMS from a programming language

b) Alternatively stand-alone DML commands is able to be applied directly (called a query language).

Types of DML:

a) High Level or Non-procedural Language:

For instance the SQL relational languages are set-oriented as well as specify what data to retrieve rather than how to retrieve it.

As well called as declarative languages.

b) Low Level or Procedural Language:

Take back data one record-at-a-time;

Constructs such as looping are essential to retrieve multiple records along with positioning pointers.

DBMS Interfaces:

a) Stand alone queries language interfaces

Instance- Inserting SQL queries at the DBMS interactive SQL interface (example SQL*Plus in ORACLE)

b) Programmer edge for embedding DML in programming languages

c) User friendly interfaces

d) Forms-based, Menu-based, graphics-based etc.

DBMS Programming Language Interfaces:

• Programmer edge for embedding DML in programming languages:
• Embedded Approach example embedded SQL (for C,C++ etc.) SQLJ (for Java)
• Procedure Call Approach example JDBC for Java ODBC for other programming languages
• Database Programming Language Approach:

Example ORACLE has PL/SQL a programming language based on SQL language incorporates SQL and its data types as integral components

User-Friendly DBMS Interfaces:

• Menu-based well-liked for browsing on the web
• Forms-based intended for naïve users
• Graphics-based (Drag and Drop and Point and Click etc.)
• Usual language requests in written English
• Combinations of the above for instance both menus and forms used extensively in Web database interfaces

Other DBMS Interfaces:

• Speech as Input as well as Output
• Parametric interfaces example bank tellers using function keys
• Interfaces for the DBA
• Web Browser as an interface
• Creating user accounts and granting authorizations
• Changing schemas or access paths
• Setting system parameters

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