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Q. Describe how an ER schema can be represented by relation schemas and constraints arising from ER design can be mapped to constraints on a relation schema.
The entity relationship data model is based on a perception of a real world that consists of basic objects called entities and of relationships among these objects. An entity is thing or object in the real world that is distinguishable from other objects. For eg., each person is an entity and band accounts can be considered as entities. Entities are described in a database by set of attributes. For eg., the attributes account number and balance may describe one particular acconunt in a bank and they form attributes of the account entity set. An extra attribute customer id is used to uniquely identify customers. A relationship is an association among several entities. For eg., a depositor relationship associates a customer with each account that he has. The set of all entities of the same type and the set of all relationship of the same type are called entity set and relationship set respectively. The overall logical structure of a database can be expressed graphically by and ER diagram, which is buily up using : R ectangles - which represent entity sets Ellipses - which represent attributes Diamonds - which represent relationships Lines - which represent link attributes to entity sets. Each component is labelled with the entity or relationship that it represents. Constraints to which the contents of database must confirm. For eg., mapping cardinalities, which express the number of entities to which another entity can be asociated via a relationship set.
Logical Operators Rules of Precedence: Order evaluated Operator 1 All comparison operators 2
At its most essential level the DBMS architecture can be divide into two parts: the back end and the front end. The back end is responsible for managing the physical database an
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Locks: Serialisabilty is just a test whether a given interleaved schedule is ok or has a concurrency related trouble. Though, it does not make sure that the interleaved concurrent
Example: RELATIONAL SCHEMA for PERSON: PERSON (PERSON_ID: integer, NAME: string, AGE: integer, ADDRESS: String) RELATION INSTANCE In this instance, m = 3 and n = 4
example of embedded SQL query
Describe the primary key functions? Primary Key : The primary key is an attribute or a set of attributes in which uniquely identify a specific example of an entity. Every entit
What is called as recursive partitioning? The system repeats the splitting of the input unless each partition of the build input fits in the memory. Such partitioning is known
What is Oracle databse structure? Oracle database structure: The relational model has three main aspects: Structures: Structures are well-defined objects which store th
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