Relational databases

Created by wdarrell 

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database management system (DBMS)

the program that manages and controls the data and the interfaces between the data and the application programs

database system

the combination of the database, the database management system, and the application programs that access the database through the database management system

online analytical processing (OLAP)

Tools that provide access to information stored in a data warehouse by using queries to investigate hypothesized relationships

record layout

A document that illustrates the arrangement of items of data in input, output, and file records

logical view

The manner in which a user or programmer conceptually organizes, views, and understands the relationships among data items

physical view

the way data are physically arranged and stored in the computer system

schema

(1) A description of the data elements in a database, the relationships among the data elements, and the structure or overall logical model used to organize and describe the data

conceptual-level schema

The organization-wide view of the entire database. It lists all data elements in the database and the relationships between them

external-level schema

An individual user's or application program's view of a subset of the organization's database. Each of these individual user views is also referred to as a subschema.

subschema

(1) a subset of the schema that includes only those data items used in a particular application program or by a particular user. (2) the way the user defines the data and the data relationships.

internal-level schema

a low-level view of the entire database describing how the data are actually stored and accessed. it includes information about record layouts, definitions, addresses, indexes, and so forth.

data dictionary

a description of each data element that is stored in the database. For example, customer numbers are stored in the database and there is a record in the data dictionary describing that data element

data definition language (DDL)

A database management system language that ties the logical and physical views of the data together. It is used to build the data dictionary, initialize or create the database, describe the logical views for each individual user or programmer, and specify any limitations or constraints on security imposed on database records or fields

data manipulation language (DML)

a dbms language used to create, read, update, and delete items in the database

data query language (DQL)

A high-level, English-like, DBMS language that retrieves, sorts, orders, and presents subsets of the database in response to user queries

report writer

A language that simplifies report creation. Typically, users need only specify which data elements they want printed and how the report should be formatted. They search the database, extract the specified data items, and print them according to the user-specified format.

data model

an abstract representation of the contents of a database

relational data model

A database model in which all data elements are logically viewed as being stored in the form of two-dimensional tables called "relations". In these tables each row represents a unique entity or record. Each column represents a field where the record's attributes are stored. The table serve as the building blocks from which data relationships can be created

tuple

A row in a relation. contains data about a specific occurrence in a database table. For example, each row in the inventory table contains all the pertinent data about a particular inventory item

primary key

the attribute, or combination of attributes, that uniquely identifies a row in database table. Used to distiguish, order, and reference records in a database

foreign key

an attribute appearing in one table that is itself the primary key of another table. Used to link tables

update anomaly

A problem that can arise in a poorly designed relational database. If attributes that are not characteristics of the primary key of a relation are stored in that table, then that data item is stored in many different rows. For example, if customer addresses are stored in the sales invoice table, then the address for a given customer is stored many times (once for each sale). Consequently, if the value of that data item is not changed in every row in which it is stored, inconsistencies in the database will result.

insert anomaly

A problem that can arise in a poorly designed relational database when attributes that are not characteristics of the primary key of a relation are stored in that table. The problem arises because new information about those attributes cannot be entered in the database without violating integrity rules. For example, assume that information about vendors is only stored as part of the purchases table. Data about potential new vendors, or about alternate supliers, could not be added until a purchase from them was made. Otherwise, the purchase order number column, the primary key of the purchases table, would have a null value, violating the entity integrity rule.

delete anomaly

a problem that can arise in a poorly designed relational database when attributes that are not characteristics of the primary key of a relation are stored in the table. deleting a row from that table may result in the loss of all info about those attributes that are not characteristics of the primary key. For ex, if customer address are only stored in the sales invoice table, then deleting the row representing the only sale to a particular customer results in the loss of all info about that customer.

relational database

A database model in which all data elements are logically viewed as being stored in two-dimensional tables called relations. In these tables each row represents a unique entity or record. Each column represents a field where the record's attributes are stored. The tables serve as the building block from which data relationships can be created.

entity integrity rule

a design constraint in a relational database, requiring that the primary key have a non-null value. this ensures that a specific object exists in the world and can be identified by reference to its primary key value.

referential integrity rule

a constraint in relational database design requiring that any non-null value of a foreign key must correspond to a primary key in the referenced table

normalization

The process of following the guidelines for properly designing a relational database that is free from delete, insert, and update anomalies.

semantic data modeling

the designer uses knowledge of business processes and information needs to create a diagram that shows what to include in the database

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