Data Management
Data management refers to the procedures used to acquire, access, and
maintain data. Three major aspects of data management are data accuracy
, data security, and data maintenance. Data accuracy (data integrity)
means that the source of the data is reliable and the data is reported
and entered correctly. Data security involves protecting data to keep
it from being misused or lost. Data maintenance refers to the procedures
used to keep data current.
The Hierarchy of Data
Data is organized in a hierarchy in which each higher level is made up of
one or more elements from the lower level preceding it. A bit is a binary
digit that usually is combined with other bits to represent data. A byte
is a combination of eight bits that can represent a character. A field is
a combination of one or more bytes and usually is the smallest item of
meaningful data. A record is a group of related fields. A file is a
collection of related records or data that is stored under a single
name. A database is a group of related files.
Sequential File Organization
Files typically are organized based on the media on which they are stored
or the manner in which they are processed. Sequential file organization,
which is used with files stored on tape, means that records are stored
sequentially, one after the other. Records are retrieved in the same order
in which they are stored; the computer cannot retrieve a record without
reading all the preceding records first.
Indexed File Organization
Indexed file organization uses a separate file, called an index, to record
the location of a record on a storage device. An index consists of a list
containing the values of one or more fields and the corresponding disk
address for each record. Indexed files can be accessed sequentially and
directly. With direct, or random, access, the system can go directly to
a record without having to read the preceding records.
Direct File Organization
Direct file organization uses a record’s key value to determine the
location on the disk where the record is stored. In a process called
hashing, a formula is used to calculate the location of a record. Once
a record is stored in its relative location within a direct file, it can
be retrieved either directly or sequentially.
Data Maintenance
Data maintenance includes processes needed to keep data current and
accurate. Records are added when additional data is needed to make the
file current. Records are changed to correct inaccurate data and to
update older data. Records are deleted when they are no longer needed.
Database Management Systems
A basic file-oriented system is made up of flat files, each of which
is independent and contains all the information needed to process the
records in that one file. A database management system (DBMS) is software
that allows data and file relationships to be created, maintained, and
reported. A database management system offers a number of advantages over
a file-oriented system including reduced data redundancy (duplication),
increased data accuracy, easier reporting, improved data security, and
reduced development time. Databases are organized according to the following
four types: hierarchical, network, relational, and object-oriented.
Hierarchical and Network Databases
In a hierarchical database, data is organized in a series like a family tree.
Each parent record can have multiple child records, but each child record can
have only one parent. All parent-child relationships are established when the
database is created in a separate process that sometimes is called generating
the database. A network database is similar to a hierarchical database except
that each child record can have more than one parent. A child record is
referred to as a member, and a parent record is referred to as an owner.
Relationships can be established among different branches of the data,
offering increased access capability for the user. Like a hierarchical
database, however, data relationships must be established prior to the
use of the database and must be redefined if fields are added or modified.
Relational and Object-Oriented Databases
In a relational database, data is organized in tables that are called
relations. The tables are further divided into rows (called tuples) and
fields (called attributes). The range of values that an attribute can
have is called a domain. With a relational database, links between tables
(files) can be established at any time, provided the tables have a common
field. An object-oriented database keeps track of objects, which are entities
that contain both data and the action that can be taken on the data.
Object-oriented databases also are designed to store unstructured data
such as photographs, video, and audio clips.
PC Database Management Systems
Popular PC database management systems include Access, Paradox, Approach,
and FoxPro. Database management systems share a number of common features
including a data dictionary, utilities, security, replication, recovery,
and a query language.
Query Languages
A query language is a simple English-like language that can be used to
specify the data seen on a report or screen display. Query-by-example
(QBE) helps to construct a query by displaying a list of fields available
in the files from which the query will be made. Three relational operations
are used to query a relational database. The select relational operation
picks certain records based on designated criteria. The project relational
operation specifies fields that will appear on the query output. The
join relational operation combines two files. One of the more widely
used query languages is Structured Query Language (SQL).
Dabase Administration
The database administrator (DBA) is the person responsible for managing all
database activities. The job of the DBA usually includes database design,
user coordination, performance monitoring, system security, data distribution
, and backup and recovery.
Guidlines for Creating Database Files
Carefully designed database files make it easier for a user to query a
database and create reports. A process called normalization is used to
organize the data in relational database files into the most efficient
and logical file relationships. The following guidelines can be applied
to both relational and flat files: design the file on paper first, include
a unique key field, use separate fields for logically distinct items, do
not create fields for information that can be derived from entries in other
fields, allow enough space for each field, and set default values for
frequently entered data.
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