Article on - Data Definition Feature of SQL and its specifications

 

 

·         The set of relations within a database must be specified to the system by means of a data definition language . Here , it means that all the forms of defining the structure and schema of a database and a relation are to be done with the help of a standard language called as a Structured Query Language .

 

·         The SQL DDL allows the provision of specification of not only a set of relations but also information on each of the relations over a database which also includes the following types :

 

1) The schema for each of the relation within the database

This means that SQL language can be used for the creation of the schema definition of each of the relation within the database over which one is working upon . For example if there are a set of associated relational tables over a database management system in the given format :

 

branch (branch_name,branch_city,assets)

customer(customer_name,customer_street,customer_city)

 

Here , one can notice that the two existing tables within the given supposed database consists of primarily two tables that is branch and customer which has the following attributes as given in the parenthesis brackets . This representative definition of the two relational tables can be practically created and implemented using the SQL language using the create table command which takes the attribute names as parameters within the database schema definition function .

 

2) The domain of values associated with each of the attribute .

So from the above picture one can notice what are the essential domain types present in SQL that support the purpose of Data Definition within a database relation . So whatever data needs to be defined and stored within the columns/attributes of a relational table they should adhere to these domain standards and any exception in the datatype and format of the data is not facilitated within the SQL scripts .

 

 

 

3) The Integrity Constraints

The purpose of defining integrity constraints upon a database is to make sure that the database consists of attributes which adhere to the definition set upon the database as per the manner prescribed upon the database as in the case wherever not null is defined , the attribute cannot have a null value within it ;

wherever the constraint primary is defined , then it will mean that the values contained within the attribute for the relation cannot having non-unique values within it but columns / attributes where primary is not declared from the beginning , those attributes / columns can contain non--unique values .. etc etc

 

4) The set of indices to be maintained for each of the relation

Tables and Relations are needed to be maintained and described for the purpose of better searching , easier access and book keeping of relational tables within the database and as such indexing is one of the key parameters while considering the case of creation / definition of the data over databases

 

5) The security and authorization of information for each of the relation

This aspect of Data definition for a database and all the relations within it is a mandatory criteria for maintenance of security of the database ; otherwise unauthorised users would access the data and make unregulated transactions or tampering which might make the purpose of database and relational database invalidated

 

6) The physical storage structure of each relation on a disk

Sometimes whenever a relational table and other associated tables are created , the physical storage limit is specified so that stack overflow and buffer overflow type of memory issues could be handled well in time or in advance . Constraints related to data size limits are also set while defining the attributes during

the table creation commands so that any issues relating to memory would be handled while data defining and storage and exceptions would not arise afterwards .