MIS Database Management System

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Database Management SystemConceptual View11/25/2008Institute of Management Sciences

Muhammad Atif Nasim

2 | P a g eDatabaseA database is a collection of related information in organizemanner.The data stored in adatabase is Constant.Database Management SystemsA database management system (DBMS) is software or a collection of software which can be

used to create, maintain and work with databases.A client/server database system is one in which the database is storedand managed by adatabase server, and client software is used torequest information from the server or to sendcommands to theserver.Uses of databasesDatabases are commonly used to store bodies of data which are toolarge to be managed onpaper or through simple spreadsheets.Most businesses use databases for accounts, inventory, personnel, andother record keeping.Databases are also becoming more widely used by home users foraddress books, cdcollections, recipe archives, etc.

There are very few fields in which databases cannot be used.Type of DatabasesFlat-file text databasesHierarchical databases such as LDAPNetwork databasesRelational databasesObject Oriented databasesDelimited text filesA delimited text file is one in which each line of text is a record, andthe fields are separatedby a known character. The character used todelimit the data varies according to the type ofdata. Common


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delimiters include the tab character (\t in Perl) or variouspunctuationcharacters. The delimiter should always be one which doesnot appear in the data.Delimited text files are easily produced by most desktop spreadsheetand databaseapplications (eg Microsoft Excel, Microsoft Access). You

can usually choose "File" then"Save As"3 | P a g eImagine a file which contains peoples' given names, surnames, andages, delimited by thepipe (|) symbol:Fred|Flintstone|40Wilma|Flintstone|36Barney|Rubble|38Betty|Rubble|34Homer|Simpson|45Marge|Simpson|39Bart|Simpson|11Lisa|Simpson|9

The file above is available in your exercises directory asdelimited.txt.Comma-separated variable (CSV) filesComma separated variable files are another format commonlyproduced by spreadsheet anddatabase programs. CSV files delimittheir fields with commas, and wrap textual data inquotation marks,allowing the textual data to contain commas if required:"Fred","Flintstone",40

"Wilma","Flintstone",36"Barney","Rubble",38"Betty","Rubble",34"Homer","Simpson",45"Marge","Simpson",39"Bart","Simpson",11"Lisa","Simpson",9CSV files are harder to parse than ordinary delimited text files. Thebest way to parse them isto use the Text::ParseWords module:

Problems with flat file databasesLockingWhen using flat file databases without locking, problems can occur if two or more peopleopen the files at the same time. This can cause data to be lost orcorrupted.If you are implementing a flat file database, you will need to handle filelocking using Perl's


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flockfunct i on.Complex dataIf your data is more complex than a single table of scalar items,managing your flat filedatabase can become extremely tedious and difficult.

EfficiencyFlat file databases are very inefficient for large quantities of data.Searching, sorting, andother simple activities can take a very long timeand use a great deal of memory and othersystem resources.

4 | P a g eHierarchical Database DefinitionA kind of {database management system} that links records togetherlike a family tree suchthat each record type has only one owner, e.g.an order is owned by only one customer.Hierarchical structures werewidely used in the first {mainframe} database

managementsystems.However, due to their restrictions, they oftencannot be used to relate structures thatexist in the real world.Network model

The network model is a database model conceived as a flexible way of representing objectsand their relationships. Its original inventor wasCharles Bachman, and it was developed intoa standard specificationpublished in 1969 by the CODASYL Consortium. Where thehierarchicalmodel structures data as a tree of records, with each record havingone parentrecord and many children, the network model allows eachrecord to have multiple parent andchild records, forming a latticestructure.

The chief argument in favour of the network model, in comparison tothe hierarchic model,was that it allowed a more natural modelling of relationships between entities. Although themodel was widelyimplemented and used, it failed to become dominant for two mainreasons.Firstly, IBM chose to stick to the hierarchical model with semi-network extensions in theirestablished products such as IMS and DL/I.Secondly, it was eventually displaced by therelational model, whichoffered a higher-level, more declarative interface. Until the early1980sthe performance benefits of the low-level navigational interfacesoffered byhierarchical and network databases were persuasive formany large-scale applications, but ashardware became faster, theextra productivity and flexibility of the relational model led tothegradual obsolescence of the network model in corporate enterpriseusageRelational Database


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A relational database is a collection of data items organized as a set of formally-described tables from which data can be accessed orreassembled in many differentways without having to reorganize thedatabase tables. The relational database wasinvented by E. F. Codd atIBM in 1970.

The standard user and application program interface to a relationaldatabase is thestructured query language (SQL). SQL statements areused both for interactivequeries for information from a relationaldatabase and for gathering data for reports.In addition to being relatively easy to create and access, a relationaldatabase has theimportant advantage of being easy to extend. Afterthe original database creation, anew data category can be addedwithout requiring that all existing applications bemodified.A relational database is a set of tables containing data fitted intopredefinedcategories. Each table (which is sometimes called a relation)contains one or moredata categories in columns. Each row contains aunique instance of data for thecategories defined by the columns. Forexample, a typical business order entrydatabase would include a tablethat described a customer with columns for name,address, phonenumber, and so forth. Another table would describe an order: product,

5 | P a g ecustomer, date, sales price, and so forth. A user of the database couldobtain a view ofthe database that fitted the user's needs. For example,a branch office manager mightlike a view or report on all customersthat had bought products after a certain date. Afinancial servicesmanager in the same company could, from the same tables, obtainareport on accounts that needed to be paid.


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When creating a relational database, you can define the domain of possible values in adata column and further constraints that may applyto that data value. For example, adomain of possible customers couldallow up to ten possible customer names but beconstrained in one

table to allowing only three of these customer names to be specifiable.

The definition of a relational database results in a table of metadata orformaldescriptions of the tables, columns, domains, and constraints.Object-Oriented Database Definition(OODB) A system offering {DBMS} facilities in an {object-orientedprogramming}environment.Data is stored as {objects} and can beinterpreted only using the {method}sspecified by its {class}.Therelationship between similar objects is preserved ({inheritance})as arereferences between objects.Queries can be faster because {joins} areoften not needed(as in a {relational database}).This is because anobject can be retrieved directly without asearch, by following its objectID. The same programming language can be used for bothdatadefinition and data manipulation.The full power of the databaseprogramming language's{type system} can be used to model {datastructures} and the relationship between thedifferent data items.{Multimedia} {applications} are facilitated because the {class}{method}s associated with the data are responsible for its correctinterpretation. OODBstypically provide better support for{versioning}.An object can be viewed as the set of all itsversions.Also,

object versions can be treated as fully fledged objects.OODBs alsoprovidesystematic support for {triggers} and {constraints} which arethe basis of {active databases}.Most, if not all, object-oriented{application programs} that have database needs will benefitfromusing an OODB. {Ode} is an example of an OODB built on {C++}.Tables and relationshipsIn a relational database, data is stored in tables. Each table containsdata about a particulartype of entity (either physical or conceptual).For instance, our sample database is the inventory and sales systemfor Acme Widget Co. Ithas tables containing data for the following entities:Table 4-1. Acme Widget Co TablesTableDescriptionstock_itemInventory items


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customerCustomer account detailssalepersonSales people working for Acme Widget Co.

Sales

Tables in a database contain fields and records. Each record describesone entity. Each fielddescribes a single item of data for that entity. Youcan think of it like a spreadsheet, with therows being the records andthe columns being the fields, thus:

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