Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
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.
(a) Explain briefly the three parts of a relational Model. (b) Contrast the following terms with an appropriate example: (i) stored attribute v/s derived attribute (ii) en
XYZ is a large chain of home entertainment rental over 100 stores distributed over all states in Australia. XYZ lends entertainment products such as movies, TV shows and games on v
Create Student DB and perform delete operation? STUDENT (name, student#, class, major) COURSE (course name, course#, credit hours, department) SECTION (section identifier, co
What is system log? What are the entries? Ans: The system log that is generally written on stable storage contains the redundant data required to recover from volatile
Give some encryption techniques? A) DES B) AES C) Public key encryption
Attribute Preservation This is a easy and obvious necessity that includes preserving all the attributes that were there in the relation that is being decomposed.
Advantages of Data Distribution The primary benefit of distributed database systems is the ability to access and share data in a reliable and efficient manner.
Modify a sequence: ALTER SEQUENCE SEQSS INCREMENT 2 MAXVALUE 3000; Removing a sequence: DROP SEQUENCE SEQSS;
Question: One of the tasks a database management system must perform is to ensure that the data is still intact in the face of software and hardware failure. This task is known
Have database built but having problems with some questions that go with the database
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!
whatsapp: +1-415-670-9521
Phone: +1-415-670-9521
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd