Explain different types of keys and relational model., Database Management System

Assignment Help:

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.


Related Discussions:- Explain different types of keys and relational model.

What is the error handling, What is the error handling Traditionally, b...

What is the error handling Traditionally, bits have been sent over line lacking any error correcting scheme in physical layer. The presence of the CPU in each modem makes it po

Forward recovery (redo), Forward Recovery (Redo): In this system the commit...

Forward Recovery (Redo): In this system the committed changes made by a transaction are reapplied to a previous copy of the database.                          In simpler

Define the term- state, State The position of object at any moment is ...

State The position of object at any moment is called state. An object can have many states depend upon time. After receiving some input instructions, the object can change its

Explain about foreign key, What is Foreign Key Foreign Key: Sometimes...

What is Foreign Key Foreign Key: Sometimes we may have to work with an attribute that does not have a primary key of its own. To recognize its rows, we have to use the primar

What is a primary key, What is a primary key? Primary key is chosen by ...

What is a primary key? Primary key is chosen by the database designer as the principal means of identifying an entity in the entity set.

Dealing with constraints violation, If the deletion violates referential in...

If the deletion violates referential integrity constraint, then three alternatives are available: Default option: - refuse the deletion. It is the job of the DBMS to describ

Subclassing, In the ER diagram, one example of subclassing is depicted foll...

In the ER diagram, one example of subclassing is depicted following the Services entity. The subclasses Item Based and Time Based are created. The entity Services gains the attribu

How does the two phase protocol ensure serializability, How does the two ph...

How does the two phase protocol ensure serializability in database schedules?   Ans:  A transaction is termed to follow the two-phase locking protocol if all locking operations

What do you mean by persistence, What do you mean by persistence? How you w...

What do you mean by persistence? How you will make your data persistent? Persistent data is the data, which has a longer lifetime than program which has created it. Enabling th

Tuples-attributes , Consider a relation s over the attributes A and B wit...

Consider a relation s over the attributes A and B with the following characteristics: 5,000 tuples with 10 tuples per page A 2-level B+ tree index on attribute

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd