1.10 The MODIFY command is used to 

DBA is fully responsible for managing and handling databases.Develop new or maintain existing databases based on specifications
• Develop, implement and maintain unit tests of database programs (i.e, SQL, etc)
• Share knowledge by effectively documenting work
• Respond quickly and effectively to production & development issues and taking responsibility for seeing those issues through resolution.
• Resolve database performance issues, database capacity issues, replication, and other distributed data issues.

• Scheme definition: the creation of the original database scheme. This involves writing a set of definitions in a DDL (data storage and definition language), compiled by the DDL compiler into a set of tables stored in the data dictionary.

   

• Storage structure and access method definition: writing a set of definitions translated by the data storage and definition language compiler

   

   

A Data Definition Language (DDL) is a computer language for defining data structures.In SQL, DDL contains commands for defining structure of data,altering and deleting structure of data.

1. Used to specify a database scheme as a set of definitions expressed in a DDL
2. DDL statements are compiled, resulting in a set of tables stored in a special file called a data dictionary or data directory.

    

    

The ability to modify a scheme definition in one level without affecting a scheme definition in a higher level is called data independence.

Data independence is of two types:-

An object-relational database (ORD) or object-relational database management system (ORDBMS) is a database management system (DBMS) similar to a relational database, but with an object-oriented database model: objects, classes and inheritance are directly supported in database schemas and in the query language. In addition, it supports extension of the data model with custom data-types and methods.
Example of a Object-Oriented Database Model.

In such a database the data and relations between them are organised in tables. A table is a collection of records and each record in a table contains the same fields.

A relational database contains multiple tables, each similar to the one in the "flat" database model. One of the strengths of the relational model is that, in principle, any value occurring in two different records (belonging to the same table or to different tables), implies a relationship among those two records.

Network model can be seen as refinement of hierarchical model.Hierarchical model provide only 1:M relationship(Means one parent and multiple childs) but now in network model it provide M:M relationship(Many To Many relationship means each child can have multiple parents and parents can have multiple childs as well).The network model is a database model conceived as a flexible way of representing objects and their relationships.

• The network model allows each record to have multiple parent and child records, forming a lattice structure.

In a hierarchical model, data is organized into a tree-like structure, implying a single upward link in each record to describe the nesting, and a sort field to keep the records in a particular order in each same-level list. Hierarchical structures were widely used in the early mainframe database management systems, such as the Information Management System (IMS) by IBM, and now describe the structure of XML documents. This structure allows one 1:N relationship between two types of data.

The table model consists of a single, two-dimensional array of data elements, where all members of a given column are assumed to be similar values, and all members of a row are assumed to be related to one another. For instance, columns for name and password that might be used as a part of a system security database. Each row would have the specific password associated with an individual user. Columns of the table often have a type associated with them, defining them as character data, date or time information, integers, or floating point numbers.