Data room the principal resources of one organization.Data stored in computer system systems form a hierarchy expanding from a solitary bit to adatabase, the significant record-keeping entity of a firm. Each higher rung the this pecking order isorganized indigenous the components below it.
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Data are logically arranged into:
1. Bits (characters)
Bit (Character) - a bit is the the smallest unit ofdata depiction (value the a little may be a 0 or 1). Eight bits do a byte i beg your pardon canrepresent a character or a special symbol in a character code.
Field - a field consists of a group ofcharacters. A data ar represents an attribute (a characteristic or quality) of someentity (object, person, place, or event).
Record - a record represents a arsenal ofattributes that define a real-world entity. A record is composed of fields, with each fielddescribing one attribute of the entity.
File - a team of related records. Records arefrequently share by the application for which lock are mostly used (employeefile). A primary key in a record is the field (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 typical pool that data records that provides data for manyapplications. The data is managed by solution software referred to as database administration systems(DBMS). The data save on computer in a database is live independence of the application programs making use of itand of the varieties of secondary storage gadgets on which it is stored.
6.2 paper Environment and also its Limitations
There are three principal methods of organizing files,of which only two administer the direct access necessary in on-line systems.
Data papers are organized so as to facilitate accessibility torecords and to ensure their efficient storage. A tradeoff between these two requirementsgenerally exists: if rapid accessibility is required, much more storage is forced to do itpossible.
Access to a document for analysis it is theessential operation on data. There room two varieties of access:
1. Sequential access - is performed when records space accessed in the order they space stored. Sequential accessibility is the main accessibility mode just in batch systems, where records are used and also updated at regular intervals.
2. Direct access - on-line handling requires direct access, by which a record deserve to be accessed there is no accessing the records between it and the start of the file. The primary an essential serves to determine the needed record.
There are three techniques of paper organization:
1. Sequential organization
2. Indexed-sequential organization
3. Straight organization
In sequential company records space physicallystored in a specified order according to a crucial field in every record.
Advantages the sequential access:
1. The is fast and also efficient as soon as dealing with large volumes the data that must be handle periodically (batch system).
Disadvantages of sequential access:
1. Requires that all new transactions it is in sorted into the ideal sequence because that sequential access processing.
2. Locating, storing, modifying, deleting, or adding records in the file requires rearranging the file.
3. This an approach is too slow-moving to manage applications requiring immediate updating or responses.
In the indexed-sequential documents method, records arephysically stored in sequential stimulate on a magnetic disk or various other direct access storagedevice based on the vital field of every record. Each paper contains one index the referencesone or more vital fields of each data record to that storage ar address.
Direct file organization offers the more quickly directaccess come records. Once using direct accessibility methods, records carry out not need to be arranged inany details sequence on warehouse media. Qualities of the direct accessibility methodinclude:
1. Computers must keep track of the storage place of each document using a variety of direct organization techniques so that data can be retrieved when needed.
2. Brand-new transactions\" data do not have to be sorted.
3. Processing that requires instant responses or update is quickly performed.
6.3 Database setting
A database is an arranged collection the interrelateddata that serves a variety of applications in one enterprise. The database stores no onlythe worths of the qualities of various entities but also the relationships between theseentities. A database is managed by a database monitoring system (DBMS), a systems softwarethat gives assistance in controlling databases mutual by many users.
1. Helps organize data for effective access by a range of users through different accessibility needs and also for effective storage.
2. It makes it feasible to create, access, maintain, and control databases.
3. Through a DBMS, data deserve to be integrated and presented top top demand.
Advantages that a database monitoring approach:
1. Staying clear of uncontrolled data redundancy and also preventing inconsistency
2. Program-data independence
3. Flexible accessibility to shared data
4. Advantages of central control the data
6.4 level of Data definition in Databases
The user view of a DBMS becomes the basis for the datemodelling procedures where the relationships between data aspects are identified. This datamodels define the logical relationships among the data elements needed to support a basicbusiness process. A DBMS serves as a logical framework (schema, subschema, and physical)on i beg your pardon to basic the physical style of databases and the advance of applicationprograms to assistance the organization processes of the organization. A DBMS allows us todefine a database on 3 levels:
1. Schema - is an as whole logical see ofthe relationships in between data in a database.
2.Subschema - is a logical check out ofdata relationships essential to support specific end user applications programs that willaccess the database.
3.Physical - look at at exactly how data isphysically arranged, stored, and accessed top top the magnetic disks and other secondarystorage devices of a computer system.
A DBMS offers the language, called datadefinition language (DDL), for defining the database objects ~ above the 3 levels.It additionally provides a language because that manipulating the data, dubbed the data manipulationlanguage (DML), which renders it feasible to access records, readjust values ofattributes, and also delete or insert records.
6.5 Data Models or how to RepresentRelationships in between Data
A data version is a an approach for arranging databases onthe logical level, the level of the schema and also subschemas. The main problem in such amodel is just how to stand for relationships among database records. The relationship amongthe numerous individual records in databases are based upon one of several logical datastructures or models. DBMS space designed to administer end users through quick, easy accessibility toinformation save on computer in databases. Three major models include:
1. Hierarchical Structure
2. Network Structure
3. Relational Structure
Early mainframe DBMS packages used the hierarchicalstructure, in which:
1. Relationships in between records type a hierarchy or tree prefer structure.
2. Documents are dependent and arranged in multilevel structures, consists of one root record & any number of subordinate levels.
3. Relationships among the records are one-to-many, since each data facet is related just to one element over it.
4. Data facet or record at the highest possible level of the pecking order is dubbed the source element. Any type of data element can it is in accessed through moving progressively downward from the root and along the branches of the tree till the preferred record is located.
The network structure:
1. Have the right to represent more facility logical relationships, and also is still used by countless mainframe DBMS packages.
2. Enables many-to-many relationship amongst records. That is, the network model can accessibility a data facet by following one of numerous paths, because any kind of data element or record can be concerned any number of other data elements.
The relational structure:
1. Most famous of the three database structures.
2. Supplied by most microcomputer DBMS packages, and many minicomputer and mainframe systems.
3. Data elements within the database room stored in the kind of simple tables. Tables are associated if castle contain usual fields.
4. DBMS packages based on the relational design can link data elements from assorted tables to provide information come users.
Evaluation of Database Structures
|Hierarchical Data Structure||Ease with which data have the right to be stored and retrieved in structured, routine species of transactions. |
Ease v which data can be extracted for reporting purposes.
Routine varieties of transaction handling is fast and efficiently.
|Hierarchical one-to many relationships should be stated in advance, and are no flexible. Cannot quickly handle advertisement hoc requests for information. |
Modifying a ordered database structure is complex.
Great deal of redundancy.
Requires understanding of a programming language.
|Network Structure||More functional that the ordered model.Ability to administer sophisticated reasonable relationships among the records||Network many-to-many relationships must be specified in advanceUser is restricted to retrieving data that deserve to be accessed using the created links in between records. Cannot easily handle ad hoc requests for information. |
Requires knowledge of a programming language.
|Relational Structure||Flexible in the it can handle advertisement hoc details requests.Easy because that programmers to work-related with. End users deserve to use this model with litter effort or training. |
Easier to keep than the hierarchical and network models.
|Cannot process large amounts of business transactions together quickly and efficiently as the hierarchical and also network models.|
A relational database is a arsenal of tables. Such adatabase is reasonably easy for finish users to understand. Relational databases affordflexibility across the data and are simple to understand and also modify.
1. Select, i m sorry selects from a specified table the rows that satisfy a given condition.
2. Project, i beg your pardon selects indigenous a provided table the specified attribute values
3. Join, which build a brand-new table indigenous two mentioned tables.
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The power of the relational model derives native the joinoperation. The is precisely since records are concerned one one more through a joinoperation, fairly than v links, that we do not require a predefined access path. Thejoin operation is additionally highly time-consuming, requiring access to plenty of records save on computer ondisk in bespeak to find the needed records.
6.7 SQL - A Relational ask Language
Structured Query languages (SQL) has come to be aninternational standard accessibility language for defining and manipulating data in databases. Itis a data-definition-and-management language that most well-known DBMS, including somenonrelational ones. SQL might be offered as one independent query language to define the objectsin a database, get in the data into the database, and accessibility the data. The so-calledembedded SQL is also listed for programming in procedural languages (Ahost