by Dinesh Thakur Category: DBMS & RDBMS

Relation Algebra is a procedural query language for RDBMS (Relational Database Management System). An Algebra based on the set of operators (like Arithmetic operator, union, intersection relational operator, etc.) and operand. Edgar F. Codd created it for a relational database. Relational Algebra provides a fundamental query for retrieving data from databases. The retrieved result from algebra expression is a relation which formed from one or more relations. Relational Algebra specifies many operations to manipulate relations.



 
by Dinesh Thakur Category: DBMS & RDBMS

The database is the location to store the data. Firstly we used excel sheet to store the data. However, it has some problem with data integrity and redundancy problem. This problem solved by E.F. Codd proposed a model in 1970. This model was straightforward. It used the concept of mathematical relation which looks like a table.



 
by Dinesh Thakur Category: DBMS & RDBMS

dBase is a specific software product used for creating and manipulating relational databases. The term can also refer to the dBase database programming language that first appeared in the dBase product, but which is now available in many other database forms.



 
by Dinesh Thakur Category: DBMS & RDBMS

Data recovery is the art of restoring lost or damaged files. This damage can occur when your computer crashes, a virus infects, you accidentally reformat a disk that contains precious data, or you experience some other catastrophe of considerable dimension. And, at some point in your life, you're going to delete a file you really didn't mean to (believe me). The next time tragedy strikes, try running one of the many data recovery applications (powerful software written specifically for data recovery purposes) to see if it can correct the situation. Often these little jewels work magic and save your day-and your files.



 
by Dinesh Thakur Category: DBMS & RDBMS

In a computer database, the database engine is the software that does the real work of sorting the information, finding specific data that you request, and so on. The term used to refer to a separate piece of software that ran on a central computer (in this case, it is more or less synonymous with the term "back-end"). Widely used database engines include Oracle, DB2, and Sybase. Separate front-end software running on your own computer lets you tell the database engine what to do (how to sort the data, what data to find), and displays the results of your commands.



 
by Dinesh Thakur Category: DBMS & RDBMS

A database document is just a collection of information stored in computerized form. The simplest way to understand a database is to think of it like a set of 3 x 5 cards. Since the information is on your computer, though, a dick of the mouse or the stroke of a key can alphabetize those "cards," or find just the names of the people on the cards who live in a certain town, or tell you who owes how much money, and so on.



 
by Dinesh Thakur Category: DBMS & RDBMS

Attributes means characteristics. For instance, in a database or a spreadsheet you can apply attributes to each field or cell to customize your document. As a general attribute, you can choose whether it is to be a text field or a numeric field or perhaps a computed field, whose value the application calculates for you.



 
by Dinesh Thakur Category: DBMS & RDBMS

Relation schema: A set of attributes is called a relation schema (or relation scheme). A relation schema is also known as table schema (or table scheme). A relation schema can be thought of as the basic information describing a table or relation. It is the logical definition of a table. Relation schema defines what the name of the table is. This includes a set of column names, the data types associated with each column.



 
by Dinesh Thakur Category: DBMS & RDBMS

A functional dependency is an association between two attributes of the same relational database table. One of the attributes is called the determinant and the other attribute is called the determined. For each value of the determinant there is associated one and only one value of the determined.



 
by Dinesh Thakur Category: DBMS & RDBMS

The E-R model can result problems due to limitations in the way the entities are related in the relational databases. These problems are called connection traps. These problems often occur due to a misinterpretation of the meaning of certain relationships.

 
by Dinesh Thakur Category: DBMS & RDBMS

The entity set which does not have sufficient attributes to form a primary key is called as Weak entity set. An entity set that has a primary key is called as Strong entity set. Consider an entity set Payment which has three attributes: payment_number, payment_date and payment_amount. Although each payment entity is distinct but payment for different loans may share the same payment number. Thus, this entity set does not have a primary key and it is an entity set. Each weak set must be a part of one-to-many relationship set.

 
by Dinesh Thakur Category: DBMS & RDBMS

There is no standard for representing data objects in ER diagrams. Each modeling methodology uses its own notation.

All notational styles represent entities as rectangular boxes and relationships as lines connecting boxes. Each style uses a special set of symbols to represent the cardinality of connection. The symbols used for the basic ER constructs are:

 
by Dinesh Thakur Category: DBMS & RDBMS

In Entity-Relationship model a database is modeled as a collection of entities and relationship among entities. The ER model views the real world as a construct of entities and association between entities.



 
by Dinesh Thakur Category: DBMS & RDBMS

There are two techniques used for the purpose of data base designing from the system requirements. These are:

• Top down Approach known as Entity-Relationship Modeling

• Bottom Up approach known as Normalization.

 
by Dinesh Thakur Category: DBMS & RDBMS

Relational model stores data in the form of tables. This concept purposed by Dr. E.F. Codd, a researcher of IBM in the year 1960s. The relational model consists of three major components:

 
by Dinesh Thakur Category: DBMS & RDBMS

The Network model replaces the hierarchical tree with a graph thus allowing more general connections among the nodes. The main difference of the network model from the hierarchical model, is its ability to handle many to many (N:N) relations. In other words, it allows a record to have more than one parent. Suppose an employee works for two departments. The strict hierarchical arrangement is not possible here and the tree becomes a more generalized graph - a network. The network model was evolved to specifically handle non-hierarchical relationships. As shown below data can belong to more than one parent. Note that there are lateral connections as well as top-down connections. A network structure thus allows 1:1 (one: one), l: M (one: many), M: M (many: many) relationships among entities.

 
by Dinesh Thakur Category: DBMS & RDBMS

A model is a representation of reality, 'real world' objects and events, associations. It is an abstraction that concentrates on the essential, inherent aspects an organization and ignores the accidental properties. A data model represents the organization itself. It should provide the basic concepts and notations that will allow database designers and end users unambiguously and accurately to communicate their understanding of the organizational data.



 
by Dinesh Thakur Category: DBMS & RDBMS

The DBMS can be classified according to the number of users and the database site locations. These are:

On the basis of the number of users:

The database system may be multi-user or single-user. The configuration of the hardware and the size of the organization will determine whether it is a multi-user system or a single user system.



 
by Dinesh Thakur Category: DBMS & RDBMS

A DBMS performs several important functions that guarantee integrity and consistency of data in the database. Most of these functions are transparent to end-users. There are the following important functions and services provided by a DBMS:



 
by Dinesh Thakur Category: DBMS & RDBMS

A typical structure of a DBMS with its components and relationships between them is show. The DBMS software is partitioned into several modules. Each module or component is assigned a specific operation to perform. Some of the functions of the DBMS are supported by operating systems (OS) to provide basic services and DBMS is built on top of it. The physical data and system catalog are stored on a physical disk. Access to the disk is controlled primarily by as, which schedules disk input/output. Therefore, while designing a DBMS its interface with the as must be taken into account.



 

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About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.