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CS403 Database Management Systems Short Notes
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CS403 Short Notes
Atomicity states that database modifications must follow an "all or nothing" rule. Each transaction is said to be "atomic". If one part of the transaction fails, the entire transaction fails. It is critical that the database management system maintain the atomic nature of transactions in spite of any DBMS, operating system or hardware failure.
An attribute is a named column of a relation.
The sequence of events that take place behind any business process
A candidate key is a combination of attributes that can be uniquely used to identify a database record without any extraneous data. Each table may have one or more candidate keys. One of these candidate keys is selected as the table primary key.
The cardinality of a relation is the number of tuples it contains.
The community view of the database. This level describes what data is stored in the database and the relationship among the data.
Consistency states that only valid data will be written to the database. If, for some reason, a transaction is executed that violates the database’s consistency rules, the entire transaction will be rolled back and the database will be restored to a state consistent with those rules. On the other hand, if a transaction successfully executes, it will take the database from one state that is consistent with the rules to another state that is also consistent with the rules www.vustudents.ning.com
Cursors are database objects used to traverse the results of an SQL query. They point to a certain location within a recordset and allow the operator to move forward (and sometimes backward, depending upon the cursor type) through the results one record at a time.
Data can be described as "Collection of raw facts and figures".
Data Manipulation Language (DML):
A language that provide a set of operations that support the basic data manipulation operations on the data held in the database.
Data Definition Language (DDL):
A descriptive language that allows the DBA or user to describe and name the entities required for the application and the relationships that may exist between the different entities.
The description of data is known as data dictionary."Centralized repository of information about data such as meaning, relationships to other data, origin, usage, and format"
Data Independence means that upper levels are unaffected by changes to lower levels.
An integrated collection of concepts for describing data, relationships between data and constraints on the data in an organization
A repository where data from multiple databases is brought together for more complex analysis
A shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization
The overall description of the database is called database schema.
A software system that enables users to define, create and maintain the database and provides controlled access to this database.
The Degree of a relation is the number of attributes it contains.
A domain is the set of allowable values for one or more attributes.
Durability ensures that any transaction committed to the database will not be lost. Durability is ensured through the use of database backups and transaction logs that facilitate the restoration of committed transactions in spite of any subsequent software or hardware failures
An enterprise is an organization that utilizes computers and applications. In general use, enterprises refer to businesses/organizations that operate on a large scale. Applications that are designed for these organizations are often referred to as enterprise applications.
Additional rules specified by the the users or database administrators of a database.
An entity is a single object about which data can be stored. It is the "subject" of a table. Entities and their interrelationships are modeled through the use of entity-relationship diagrams.
in base relation, no attribute of a primary key can be null.
An entity-relationship diagram is a specialized graphic that illustrates the interrelationships between entities in a database.
The User's view of the database. This level describes that part of the database that is relevant to particular user.
A collection of application programs that perform services for the end users such as the production of reports. Each program defines and manages its own data.
An attribute or set of attributes within one relation that matches the candidate key of some (possibly the same) relation.
A functional dependency occurs when one attribute in a relation uniquely determines another attribute. This can be written A -> B which would be the same as stating "B is functionally dependent upon A."
The physical representation of the database on the computer. This level describes how the data is stored in the database.
Logical Data Independence:
Logical Data Independence refers to immunity of external schema to changes in the conceptual schema.
The description of data is known as Metadata.
A language that allows the user to state what data is needed rather than how it is to be retrieved.
Represents a value for an attribute that is currently unknown or is not applicable for this tuple
A standard that allows a database to be exchanged and opened by other compliant database software, independent of the database's file format or what program was originally used to create it.
Physical Data Independence:
Physical Data Independence refers to immunity of the conceptual schema to changes in the internal schema.
The candidate key that is selected to identify tuples uniquely within the relation
A language that allows the user to tell the system exactly how to manipulate the data
Deep analysis is carried out by performing multilayer queries. Because all the databases are linked, you can search for what products a store has too much of. You can then determine which of these products commonly sell with popular items, based on previous sales. After planning a promotion to move stock, you can dig deeper to see where this promotion would be most popular (and most profitable).
If foreign key exists in a relation, either the foreign key value must match a candidate key value of some tuplein its home relation or the foreign key value must be wholly null.
A relation is a table with columns and rows.
A collection of normalized relations.
A relation name followed by a set of attributes and domain name pairs.
An attribute or set of attributes that unquely identifies a tuple within a relation
The description of data is known as system catalog.
A tuple is a row of a relation.