Data space the principal resources of an organization.Data save on computer in computer system systems form a hierarchy prolonging from a single bit come adatabase, the significant record-keeping entity of a firm. Each higher rung of this hierarchy isorganized from the components below it.
You are watching: The smallest unit of information about a record in a database is called a:
Data room logically arranged into:
1. Bits (characters)
Bit (Character) - a bit is the the smallest unit ofdata depiction (value that a bit may it is in a 0 or 1). Eight bits do a byte i m sorry canrepresent a character or a distinct symbol in a character code.
Field - a field is composed of a grouping ofcharacters. A data ar represents an attribute (a characteristics or quality) the someentity (object, person, place, or event).
Record - a record represents a arsenal ofattributes that explain a real-world entity. A record is composed of fields, through each fielddescribing an attribute that the entity.
File - a group of related records. Files arefrequently classified by the application for which lock are primarily used (employeefile). A primary key in a document is the ar (or fields) whose valueidentifies a record amongst others in a data file.
Database - is an combined collection oflogically related records or files. A database consolidates records previously stored inseparate files into a usual pool that data documents that offers data for manyapplications. The data is regulated by solution software referred to as database monitoring systems(DBMS). The data save on computer in a database is elevation of the application programs making use of itand that the types of an additional storage tools on which the is stored.
6.2 record Environment and also its Limitations
There room three principal methods of arranging files,of which only two provide the direct access necessary in on-line systems.
Data files are arranged so regarding facilitate access torecords and to certain their effective storage. A tradeoff in between these two requirementsgenerally exists: if rapid accessibility is required, an ext storage is forced to do itpossible.
Access come a record for reading it is theessential operation on data. There room two varieties of access:
1. Sequential access - is performed as soon as records are accessed in the order they space stored. Sequential access is the main accessibility mode only in batch systems, where files are used and updated at constant intervals.
2. Straight access - on-line handling requires straight access, whereby a record deserve to be accessed there is no accessing the records between it and also the beginning of the file. The primary vital serves to determine the necessary record.
There room three approaches of file organization:
1. Sequential organization
2. Indexed-sequential organization
3. Direct organization
In sequential organization records space physicallystored in a mentioned order follow to a crucial field in each record.
Advantages that sequential access:
1. It is fast and also efficient once dealing with huge volumes the data that must be processed periodically (batch system).
Disadvantages that sequential access:
1. Calls for that all brand-new transactions it is in sorted into the ideal sequence for sequential access processing.
2. Locating, storing, modifying, deleting, or including records in the paper requires rearranging the file.
3. This an approach is too sluggish to take care of applications requiring prompt updating or responses.
In the indexed-sequential files method, records arephysically save in sequential stimulate on a magnetic decaying or various other direct accessibility storagedevice based on the an essential field of each record. Each file contains an index that referencesone or more vital fields of each data record to the storage place address.
Direct record organization provides the fastest directaccess to records. As soon as using direct accessibility methods, records carry out not have to be i ordered it inany certain sequence on warehouse media. Characteristics of the direct accessibility methodinclude:
1. Computer systems must store track that the storage place of each document using a selection of direct organization techniques so the data deserve to be retrieved as soon as needed.
2. Brand-new transactions" data carry out not need to be sorted.
3. Processing that requires instant responses or to update is conveniently performed.
6.3 Database environment
A database is an arranged collection the interrelateddata that serves a number of applications in an enterprise. The database stores no onlythe values of the characteristics of various entities but additionally the relationships between theseentities. A database is regulated by a database administration system (DBMS), a equipment softwarethat offers assistance in regulating databases shared by countless users.
1. Help organize data for effective access by a variety of users v different accessibility needs and for effective storage.
2. It renders it possible to create, access, maintain, and also control databases.
3. With a DBMS, data can be integrated and also presented on demand.
Advantages of a database monitoring approach:
1. Staying clear of uncontrolled data redundancy and also preventing inconsistency
2. Program-data independence
3. Flexible access to shared data
4. Advantages of central control that data
6.4 level of Data meaning in Databases
The user watch of a DBMS i do not care the basis for the datemodelling steps where the relationships in between data facets are identified. These datamodels specify the logical relationships amongst the data aspects needed to support a basicbusiness process. A DBMS serves as a logical structure (schema, subschema, and physical)on which to basic the physical style of databases and also the breakthrough of applicationprograms to support the service processes of the organization. A DBMS enables us todefine a database on three levels:
1. Schema - is an overall logical see ofthe relationships between data in a database.
2.Subschema - is a logical see ofdata relationships required to support certain end user application programs that willaccess the database.
3.Physical - look at at how data isphysically arranged, stored, and also accessed ~ above the magnetic disks and also other secondarystorage gadgets of a computer system.
A DBMS offers the language, referred to as datadefinition language (DDL), for specifying the database objects on the 3 levels.It likewise provides a language for manipulating the data, dubbed the data manipulationlanguage (DML), which renders it possible to access records, adjust values ofattributes, and delete or insert records.
6.5 Data Models or exactly how to RepresentRelationships in between Data
A data model is a technique for organizing databases onthe reasonable level, the level the the schema and subschemas. The main concern in such amodel is how to represent relationships amongst database records. The relationship amongthe countless individual records in databases are based upon one of several logical datastructures or models. DBMS are designed to administer end users with quick, easy access toinformation save on computer in databases. Three principal models include:
1. Ordered Structure
2. Network Structure
3. Relational Structure
Early mainframe DBMS packages provided the hierarchicalstructure, in which:
1. Relationships in between records kind a power structure or tree prefer structure.
2. Records are dependent and also arranged in multilevel structures, consist of of one root record & any variety of subordinate levels.
3. Relationships amongst the documents are one-to-many, because each data element is related only to one element above it.
4. Data facet or record at the highest possible level of the power structure is dubbed the root element. Any type of data aspect can it is in accessed by moving increasingly downward indigenous the root and also along the branches that the tree till the preferred record is located.
The network structure:
1. Deserve to represent more complicated logical relationships, and is still supplied by countless mainframe DBMS packages.
2. Enables many-to-many relationship amongst records. That is, the network model can accessibility a data aspect by complying with one of several paths, because any data element or record have the right to be concerned any variety of other data elements.
The relational structure:
1. Most famous of the three database structures.
2. Used by many microcomputer DBMS packages, and many minicomputer and also mainframe systems.
3. Data facets within the database are stored in the form of basic tables. Tables are related if lock contain usual fields.
4. DBMS packages based on the relational design can connect data elements from miscellaneous tables to carry out information come users.
Evaluation that Database Structures
|Hierarchical Data Structure||Ease with which data can be stored and also retrieved in structured, routine species of transactions. |
Ease with which data can be extracted because that reporting purposes.
Routine species of transaction handling is fast and efficiently.
|Hierarchical one-to many relationships need to be specified in advance, and also are not flexible. Cannot easily handle ad hoc requests for information. |
Modifying a hierarchical database framework is complex.
Great transaction of redundancy.
Requires understanding of a programming language.
|Network Structure||More functional that the hierarchical model.Ability to carry out sophisticated reasonable relationships among the records||Network many-to-many relationships should be mentioned in advanceUser is minimal to retrieving data that can be accessed utilizing the developed links between records. Cannot conveniently handle advertisement hoc requests for information. |
Requires understanding of a programming language.
|Relational Structure||Flexible in that it have the right to handle ad hoc information requests.Easy for programmers to occupational with. End users deserve to use this design with litter initiative or training. |
Easier to keep than the hierarchical and also network models.
|Cannot process big amounts of company transactions together quickly and efficiently as the hierarchical and also network models.|
A relational database is a repertoire of tables. Together adatabase is reasonably easy for end users to understand. Relational databases affordflexibility throughout the data and are easy to understand and modify.
1. Select, i beg your pardon selects indigenous a specified table the rows that satisfy a given condition.
2. Project, which selects native a provided table the stated attribute values
3. Join, which build a brand-new table from two mentioned tables.
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The strength of the relational design derives indigenous the joinoperation. The is precisely due to the fact that records are pertained to one one more through a joinoperation, quite than through links, that we execute not require a predefined accessibility path. Thejoin procedure is also highly time-consuming, requiring accessibility to many records save ondisk in order to find the needed records.
6.7 SQL - A Relational questions Language
Structured Query languages (SQL) has become aninternational standard accessibility language because that defining and manipulating data in databases. Itis a data-definition-and-management language the most well-known DBMS, including somenonrelational ones. SQL might be offered as an independent ask language to define the objectsin a database, get in the data into the database, and accessibility the data. The so-calledembedded SQL is also noted for programming in procedural languages (Ahost