Overview of Database Languages and Architectures:
Overview
of Database Languages and Architectures:
The data model
It
is
the collection of conceptual tools that can be used for describing
the structure of data in the database. A
data model provides a way to describe the design of a database at the
physical, logical and view levels. Representation of data includes
the data types, constraints, relationships and basic operations of
the data.
The
data models in the DBMS can be categorized into two:
-
High level or Data Conceptual Model
-
Low level or Physical Data Model
The high-level data model provides concepts that are closed to the user perceive data.
Low Level or Physical Data Model
The low-level data model provides concepts that may be understood by end users but that is not too far removed from the way, data is organized within the computer.
Conceptual Data Model Terms
There are three terms in the conceptual data models. They are:-
Entity
-
Attribute
-
Relationship
The entity represents a real world
object.
eg: Student, Employee
Attribute
The attribute represents the properties
of the entity.
eg: Student name, Employee name.
Relationship
The relationship represents the
association among two or more entities.
I hope this article might be helped you
to understand the basics of types of data models in DBMS.
Three Level Architecture of DBMS
Following are the three
levels of database architecture,
1. Physical Level
2. Conceptual Level
3. External Level
1. Physical Level
2. Conceptual Level
3. External Level
In the above diagram,
-
It shows the architecture of DBMS.
-
Mapping is the process of transforming request response between various database levels of architecture.
-
Mapping is not good for small database, because it takes more time.
-
In External / Conceptual mapping, DBMS transforms a request on an external schema against the conceptual schema.
-
In Conceptual / Internal mapping, it is necessary to
transform the request from the conceptual to internal levels.
-
Physical level describes the physical storage structure of data in database.
-
It is also known as Internal Level.
-
This level is very close to physical storage of data.
-
At lowest level, it is stored in the form of bits with the physical addresses on the secondary storage device.
-
At highest level, it can be viewed in the form of files.
-
The internal schema defines the various stored data types.
It uses a physical data model.
-
Conceptual level describes the structure of the whole database for a group of users.
-
It is also called as the data model.
-
Conceptual schema is a representation of the entire content of the database.
-
These schema contains all the information to build relevant external records.
-
It hides the internal details of physical storage.
-
External level is related to the data which is viewed by individual end users.
-
This level includes a no. of user views or external schemas.
-
This level is closest to the user.
- External view describes the segment of the database that is required for a particular user group and hides the rest of the database from that user group.
Components of a DBMS
The figure is divided into two halves.
The top half of the figure refers to the various users of the database environment and their interfaces. The lower half shows the internals of the DBMS responsible for storage of data and processing of transaction. The database and the DBMS catalog are usually stored on disk.Access to the disk is primarily controlled by operating system(OS).which inclues disk input/Output.A higher level stored data manager module of DBMS controls access to DBMS information that is stored on the disk. If we consider the top half of the figure, It shows interfaces to DBA staff, casual users, application programmers and parametric users
The DDL compiler processes schema definitions, specified in the DDL,and stores the description of the schema in the DBMS Catalog..The catalog includes information such as names and sizes of the sizes of the files, data types of data of data items. Storage details of each file, mapping information among schemas and constraints. Casual users and persons with occasional need of information from database interact using some for of interface which is interactive query interface. The queries are parsed, analysed for correctness of the operations for the model. the names of the data elements and so on by a query compiler that compiles them into internal form. The internal query is subjected to query optimization.
The query optimizer is concerned with rearrangement and possible recording of operations, eliminations of redundancies. Application programmer writes programs in host languages. The precompiler extracts
DML commands from an application program
