Chapter Summary
n The ANSI-SPARC database architecture uses three levels of abstraction: external, conceptual, and internal.
The external level consists of the users’ views of the database. The conceptual level is the community view
of the database. It specifies the information content of the entire database, independent of storage considerations.
The conceptual level represents all entities, their attributes, and their relationships, as well as
the constraints on the data, and security and integrity information. The internal level is the computer’s view
of the database. It specifies how data is represented, how records are sequenced, what indexes and pointers
exist, and so on.
n The external/conceptual mapping transforms requests and results between the external and conceptual
levels. The conceptual/internal mapping transforms requests and results between the conceptual and
internal levels.
n A database schema is a description of the database structure. Data independence makes each level immune
to changes to lower levels. Logical data independence refers to the immunity of the external schemas to
changes in the conceptual schema. Physical data independence refers to the immunity of the conceptual
schema to changes in the internal schema.
n A data sublanguage consists of two parts: a Data Definition Language (DDL) and a Data Manipulation
Language (DML). The DDL is used to specify the database schema and the DML is used to both read and
update the database. The part of a DML that involves data retrieval is called a query language.
n A data model is a collection of concepts that can be used to describe a set of data, the operations to manipulate
the data, and a set of integrity constraints for the data. They fall into three broad categories: object-based
data models, record-based data models, and physical data models. The first two are used to describe data at
the conceptual and external levels; the latter is used to describe data at the internal level.
n Object-based data models include the Entity–Relationship, semantic, functional, and object-oriented models.
Record-based data models include the relational, network, and hierarchical models.
n Conceptual modeling is the process of constructing a detailed architecture for a database that is independent
of implementation details, such as the target DBMS, application programs, programming languages, or any
other physical considerations. The design of the conceptual schema is critical to the overall success of the
system. It is worth spending the time and energy necessary to produce the best possible conceptual design.
n Functions and services of a multi-user DBMS include data storage, retrieval, and update; a user-accessible
catalog; transaction support; concurrency control and recovery services; authorization services; support for
data communication; integrity services; services to promote data independence; utility services.
n The system catalog is one of the fundamental components of a DBMS. It contains ‘data about the data’, or
metadata. The catalog should be accessible to users. The Information Resource Dictionary System is an ISO
standard that defines a set of access methods for a data dictionary. This allows dictionaries to be shared and
transferred from one system to another.
n Client–server architecture refers to the way in which software components interact. There is a client process
that requires some resource, and a server that provides the resource. In the two-tier model, the client handles
the user interface and business processing logic and the server handles the database functionality. In the Web
environment, the traditional two-tier model has been replaced by a three-tier model, consisting of a user interface
layer (the client), a business logic and data processing layer (the application server), and a DBMS (the
database server), distributed over different machines.
n A Transaction Processing (TP) Monitor is a program that controls data transfer between clients and servers
in order to provide a consistent environment, particularly for online transaction processing (OLTP). The
advantages include transaction routing, distributed transactions, load balancing, funneling, and increased
reliability.
n The ANSI-SPARC database architecture uses three levels of abstraction: external, conceptual, and internal.
The external level consists of the users’ views of the database. The conceptual level is the community view
of the database. It specifies the information content of the entire database, independent of storage considerations.
The conceptual level represents all entities, their attributes, and their relationships, as well as
the constraints on the data, and security and integrity information. The internal level is the computer’s view
of the database. It specifies how data is represented, how records are sequenced, what indexes and pointers
exist, and so on.
n The external/conceptual mapping transforms requests and results between the external and conceptual
levels. The conceptual/internal mapping transforms requests and results between the conceptual and
internal levels.
n A database schema is a description of the database structure. Data independence makes each level immune
to changes to lower levels. Logical data independence refers to the immunity of the external schemas to
changes in the conceptual schema. Physical data independence refers to the immunity of the conceptual
schema to changes in the internal schema.
n A data sublanguage consists of two parts: a Data Definition Language (DDL) and a Data Manipulation
Language (DML). The DDL is used to specify the database schema and the DML is used to both read and
update the database. The part of a DML that involves data retrieval is called a query language.
n A data model is a collection of concepts that can be used to describe a set of data, the operations to manipulate
the data, and a set of integrity constraints for the data. They fall into three broad categories: object-based
data models, record-based data models, and physical data models. The first two are used to describe data at
the conceptual and external levels; the latter is used to describe data at the internal level.
n Object-based data models include the Entity–Relationship, semantic, functional, and object-oriented models.
Record-based data models include the relational, network, and hierarchical models.
n Conceptual modeling is the process of constructing a detailed architecture for a database that is independent
of implementation details, such as the target DBMS, application programs, programming languages, or any
other physical considerations. The design of the conceptual schema is critical to the overall success of the
system. It is worth spending the time and energy necessary to produce the best possible conceptual design.
n Functions and services of a multi-user DBMS include data storage, retrieval, and update; a user-accessible
catalog; transaction support; concurrency control and recovery services; authorization services; support for
data communication; integrity services; services to promote data independence; utility services.
n The system catalog is one of the fundamental components of a DBMS. It contains ‘data about the data’, or
metadata. The catalog should be accessible to users. The Information Resource Dictionary System is an ISO
standard that defines a set of access methods for a data dictionary. This allows dictionaries to be shared and
transferred from one system to another.
n Client–server architecture refers to the way in which software components interact. There is a client process
that requires some resource, and a server that provides the resource. In the two-tier model, the client handles
the user interface and business processing logic and the server handles the database functionality. In the Web
environment, the traditional two-tier model has been replaced by a three-tier model, consisting of a user interface
layer (the client), a business logic and data processing layer (the application server), and a DBMS (the
database server), distributed over different machines.
n A Transaction Processing (TP) Monitor is a program that controls data transfer between clients and servers
in order to provide a consistent environment, particularly for online transaction processing (OLTP). The
advantages include transaction routing, distributed transactions, load balancing, funneling, and increased
reliability.
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