21) What Is DDL (Data Definition Language), VDL (View Definition Language) and SDL (Storage Definition Language)?
Answer: A database schema is specified by a set of definitions expressed by a special language called DDL. It is used by DBA and database designers to specify the conceptual schema of a database.
In many DBMSs, the DDL is also used to define internal and external schemas (views). Also in some DBMSs, separate storage definition language (SDL) and view definition language (VDL) are used to define internal and external schemas.
VDL (View Definition Language) specifies user views and their mappings to the conceptual schema.
SDL (Storage Definition Language) is to specify the internal schema. This language may specify the mapping between two schemas.
SDL is typically realized via DBMS commands provided to the DBA and database designers
22) What Is Data Storage - Definition Language?
Answer: The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage-definition language.
23) What Is DML (Data Manipulation Language) and DML Compiler?
Answer: DML enables user to access or manipulate data from database as organized by appropriate data model.
Types of DML are:
- Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.
- Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data. Example: SQL.
DML Compiler translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.
24) What Is DDL Interpreter?
Answer: It interprets DDL statements and records them in tables containing metadata.
25) What Is Data Model, E-R MODEL & Object Oriented Model?
Answer: A data model is a collection of conceptual tools for describing data, data relationships data semantics and constraints.
E-R model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.
ER Model has three main concepts:
- Entities (and their entity types and entity sets).
- Attributes (simple, composite, multi valued).
- Relationships (and their relationship types and relationship sets).
Object Oriented model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.
ALSO CHECK THE BELOW FAQ's:
26) What Is An Entity, Entity Type & An Entity Set?
27) What Is An Attribute? Also Define What Is A Domain?
28) What Are The Different Types Of Attributes In DBMS?
29) Differentiate Between Simple, Composite & Multi-Valued Attributes In DBMS?
30) What Are Relation Schema & A Relation?
31) What Is Degree Of A Relation?
32) Discuss The Properties Of A Relation?
33) What Is Relationship, Relationship Type & Relationship Set?
34) What Is Degree Of Relationship Type?
35) What Is A Recursive Relationship Type?
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