C192

A DBMS must furnish a mechanism that will ensure either that all the updates corresponding to a given transaction are made or that none of them is made.

transaction support

The most common physical data model are:

unifying model ; frame memory.

A DBMS should provide a set of utility services.

utility services

Some benefits of a system catalog are:

-information about data can be collected and stored centreally; -the meaning of data can be defined; -communication is simplified; -redundancy and inconsistencies can be identified more easily as the data is centralised; -changes to the database can be recorded; -the impact of a change can be determined before it is implemented ; -security can be enforced; -integrity can be ensured; -audit information can be provided.

Typically , the system catalog stores:

-names,types,and sizes of data items; -names of relationships; -integrity constraints on the data; -names of authorized users who have access to the data; -the data items that each user can access and the types of access allowed; for example, insert, update, delete, or read access;' -external,conceptual,and internal schemas and the mappings between the schemas; -usage statistics, shuch as the frequencies of transactions and counts on the number of accesses made to objects in the database.

The fundamental function of a DBMS:

-store ; -retrieve; -update data in database.

The three related data models:

1.an external data model, to represent each user's view of the organization,sometimes called the Universe of Discourse(UoD); 2.a conceptual data model, to represent the logical (or community) view that is DBMS-independent; 3.an internal data model, to represent the conceptual schema in such a way that it can be understood by the DBMS.

network and hierarchical systems adopt a approach(that is , they specify how the data is to be retrieved)

navigational

The conceptual level represents:

=all entities, their attributes, and their relationships; =the constraints on the data; =semantic information about the data; =security and integrity information.

Some of the more common types of object based data model are:

=entity-relationship(ER); =semantic; =functional; =object-oriented;

Data manipulation operations usually include the following:

=insertion of new data into the database; =modification of data stored in the database; =retrieval of data contained in the database; =deletion of data from the database.

The internal level is concerned with such things as:

=storage space allocation for data and indexes; =record descriptions for storage(with stored sizes fir data items); =record placement; =data compression and data encryption techniques.

A conceptual/internal mapping enables the DBMS to find the actual record or combination of records in physical storage that constitute a .... record in the conceptual schema,together with any constraints to be enforced on the operations for that logical record.

A logical record

the architecture of most commercial DBMSs available today is based to some extent on the so -called : ____architecture.

ANSI-SPARC architecture.

The community view of the database. This level describes what data is stored in the database and the relationships among the data.

Conceptual level

The .... language is used to specify the database shcema

DDL

A language that allows the DBA or user to describe and name the entities, attributes, and relationships required for the application, together with any associated integrity and security constraints.

DDL(the data definition language)

The ... is used to both read and update the database.

DML

A language that provides a set of operations to support the basic data manipulation operations on the data held in the database.

DML ( data manipulation language)

These languages are called .... because they do not include constructs for all computing needs, such as conditional or iterative statements, which are provided by the high-level programming languges.

Data Sublanguages

An integrated collection of concepts for describing and manipulationg data, relationships between data and constraints on the data in an organization

Data model

The users' view of the database. This level describes that part of the database that is relevant to each user.

External level

.... is a software tool that can be used to control and document an organization's information sources.

IRDS

The ISO has adopted a standard for data dictionaries called ....

Information Resource Dictionary System(IRDS)

The physical representation of the database on the computer. This level describes how the data is stored in the database.

Internal level

The immunity of the external schemas to changes in the conceptual schema.

Logical data independence

At language that allows the user to state what data is needed a rather than how it is to be retrieved.

Nonprocedural DML

The immunity of the conceptual schema to changes in the internal schema.

Physical data independence

.... data models describe how data is stored in the computer,representing information such as record sturctures, record orderings, and access paths.

Physical data models

a ..... is an association between entities

Relationship

The .... level provides both the mapping and the desired independence between the external and internal levels.

The conceptual level

A data sublanguage consists of two parts:

a Data Definition Language (DDL) and a Data Manipulation Language (DML).

A database system

a collection of application programs that interact with the database along with the DBMS and the database itself.

The conceptual schema is related to the internal schema through a ....

a conceptual/internal mapping.

A major objective for the three-level architecture is to provide .... , which means that upper levels are unaffected by changes to lower levels.

a data independence

The data in the database at any particular point in time is called a

a database instance.

A .... part , defining the types of operation that are allowed on the data ( this includes the operations that are used for updating or retrieving data from the database and for changing the structure of the database).

a manipulative part

In a ....-.... model , the database consists of a number of fixed-format records,possibly of differing types.

a record-based

a set of ...... ..... , which ensures that the data is accurate.

a set of integrity constraints

A .... part , consisting of a set of rules according to which databases can be constructed.

a structural part

A data model can be thought of as comprising three components:

a structural part; a maniputalive part ; a set of integrity constrains

A DBMS must furnish a catalog in which descriptions of data items are stored and which is accessible to users.

a user-accessible catalog.

An .... is a property that describes some aspect of the object that we wish to record.

an attribute

An ..... is a distinct object ( a person, place,thing,concept,event) In the organization that is to be represented in the database

an entity

An instance is called an .... of the database.

an extension (or state)

Three level of abstraction , that is , three distinct levels at which data items can be described. The levels form a three-level architecture comprising an .....

an external , a conceptural , and an internal level.

An .... is a facility for producing a program that interfaces with the database.

application generator

The records in network model are organized as generalized graph structures with records appearing as .... ( also called .... ) and sets as .... in the graph.

as nodes ( also called segments) and sets as edges

A DMBS must furnish a mechanism to ensure that only authorized users can access the database.

authorization services

A DBMS must furnish a mechanism to ensure that the database is updated correctly when multiple users are updating the database concurrently.

concurrency control services

The terms .... and ..... are also used to describe the system catalog, although the term "data dictionary" usually refers to a more general software system than a catalog for a DBMS.

data dictionary and data directory

A .... is an interactive facility for rapidly crating data input and display layouts for screen forms.

forms generators

Relational systems adopt a ..... approach to database processing (that is, they specify what data is to be retrieved)

declarative

Nonprocedural languages are also called ...

declarative languages.

The way users perceive(become aware or conscious of (something); come to realize or understand) the data is called the ...

external level

There are three different types of schema in the database and these are defined according to the levels of abstraction of the three-level architecture :

external schemas; conceptual schema; internal schema.

A .... is a facility to retrieve data from the database and display the data as a graph showing trends and relationships in the data.

graphics generator

The .... model is a restricted type of network model.

hierarchical model

The high-level language is sometimes referred to as the ...

host language

A DBMS must furnish a means to ensure that both the data in the database and changes to the data follow cetrain rules.

integrity services

A database application

is simply a program that interacts with the database at some point in its execution.

There are two main types of a report generator

language-oriented and visually oriented

There are two kinds of data independence :

logical and physical.

A system catalog, or data dictionary, is a repository of information describing the data in the database ;it is the "data about the data" or the .....

metadata

The system catalog integrates the ...... , which is data that describes the objects in the database and makes it easier for those objects to be accessed or manipulated.

metadata

In the ... model , data is represented as collections of records, and relationships are represented by sets.

network model

Most data sublanguages also provide ..... or ..... commands that can be input directly from a terminal.

nonembedded or interactive

Data models fall into three broad categories:

object-based,record-based,and physical data models.

Below the internal level there is a ...... level that may be managed by the operating system under the direction of the DBMS.

physical level

A Language that allows the user to tell the system what data is needed and exactly how to retrieve the data.

procedural DML

DMLs are distinguished by their underlying retrieval constructs by two types:

procedural and nonprocedural

The part of a DML that Involves data retrieval is colled a :

query language

...-.. (logical) data models are used to specify the overall structure of the database and a higher-level description of the implementation.

record-based

A DMBS must furnish a mechanism for recovering the database in the event that the database is damaged in any way .

recovery services

The .... data model is based on the concept of mathematical relations

relational data model

A .... is a facility for creating reports from data stored in the database.

report generator

A DBMS must include facilities to support the independence of programs from the actual sturcture of the database .

services to promote data independence

A system view called ...

shcema

A user views called ...

subschemas

A DBMS must be capable of integrating with communication software.

support for data communication

This schema describes all the entities, attributes, and relationships together with integrity constraints.

the conceptual schema

The overall description of the database is called the :

the database schema.

Each external schema is related to the conceptual schema by the ....

the external/ conceptual mapping.

This mapping enables the DBMS to map names in the user's view to the relevant part of the conceptual schema.

the external/ conceptual mapping.

The schema is sometimes called the .... of the database

the intension

There are a three principal types of record-base logical data model:

the relational data model, the network data model, and the hierarchical data model.

The result of the compilation of the DDL statements is a set of tables stored in special files collectively called the ....

the system catalog.