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Relational Model: The relational model uses a collection of tables to represent both data and the relationships among those data. Each table has multiple columns and each column has a unique name. Figure presents a sample relational database comprising three tables: One shows details of bank customer, the second shows accounts belong to which customers. The relational is an example of a record based model. Record based models are so named because the database is structured in fixed format records of several types. Each table contains of a particular types. Each types defines a fixed number of fields or attributes. The relational data model is the most widely used data model, and a vast majority of current database systems are based on the relational model. The relational model is at a lower level of abstractions than the E-R model.
Other Data Models: The object- oriented data model is another data model that has seen increasing attention. The object- oriented model can be seen as extending the E-R model with notions of encapsulation, methods, and object identity. Historically, two other data models, the network data model and the hierarchical data model, preceded the relation of data model. These models were tied closely to the underlying implementation, and complicated the task of modeling data. Semi structured data models permit the specification of data where indivisible data items of the same type may have different sets of attributes. This is in contrast with the data models mentioned earlier, where every data item of a particular type must have the same set of attributes. The extensible markup language (XML) is widely used to represent semi- structured data.
Keys:
Superkey: It is a set of one or more attributes that taken collectively; allow us to identify an entity set. Candidate key: Superkeys from which no proper subset is a superkey. Such minimal superkeys are called candedate keys.
Primary key: Allows us to distinguish between different entities of set. It must be chosen s.t. its attributes are never or rarely changed.
Foreign Key: When relation schema say r1may include among its attributes the primary key of another relation schema say r2. This attribute is called foreign key from r1, referencing r2, we sometimes define a primary key and sometimes not but there also candidate key will exist. Two attributes taken together can make a key called as composite primary key.
Explain the Fundamental concepts of object-orientation Software developers, data base administrators (DBAs) need to be familiar with fundamental concepts of object-orientation.
Differentiate between natural join and outer join? Natural join is a binary operator which is written as (R * S) where as R and S are relations. The output of the natural join
To do the division operation R1 ÷ R2, R2 should be a correct subset of R1. In the following example R1 have attributes A and B and R2 have only attribute B so R2 is a correct subse
A software contract and consultancy firm maintains details of all the various projects in which its employees are currently involved. These details comprise: Employee Numbe
Make SQL statements for the following scenarios. Your response should contain SQL statement, output and any other assumptions you have made to arrive at the answer. For Colorado cu
Physical Database Design Issues The database design includes the process of logical design with the use of E-R diagram, normalisation, etc., followed by the physical design.
What are the states of transaction? The states of transaction are:- a) Active b) Partially committed c) Failed d) Aborted e )Committed f) Terminated
Example- Search the salary of employees who are not 'ANALYST' but get a salary below than or equal to any people employed as 'ANALYST'. SELECT EMPNO, ENAME, JOB, SAL FROMEMP
how to write tables and drow E-R diagrams for hosiptal management system and how to normalize and cardinalities?
With the linear commit protocol, sites are connected in a chain, and the subtransaction at the left-hand end of the chain initiates the protocol. Propose a crash recovery protocol
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