Use of ICT in Data Management AS Applied ICT

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Back to Contents Back to Contents What is a database?  It is a collection of related data.  It consists of records and fields; each record contains the same set of fields.  One field contains one piece of information.  What is the purpose of DBMS? What is the purpose of DBMS

Back to Contents Back to Contents Database Management System (DBMS) This is a kind of software that is used to manage database systems: – Structure of individual data files – Relationships between data items + between data files – How data is searched (interrogated) – Properties of the database (queries, updating or amendments)

Back to Contents Back to Contents Sequential Files Records are stored one after the other in the order they were added to the storage medium. Storage Medium: Magnetic Tape Two ways in which records can be arranged: 1. Have the records in an order using a key field. What is a key field? Its is unique for every record. It is required to ensure that you don’t have any duplicates. This type of type of sequential is called ordered sequential. This type of type of sequential is called ordered sequential.

Back to Contents Back to Contents Sequential Files 2.Another way is to arrange the records in no particular order This is type of sequential is called unordered sequential. Another name for an unordered file is serial file. There is only one way of accessing the data: by going through each record one by one.

Back to Contents Back to Contents Sequential Files Ordered file -- > data is put in order of a key field (For example: customer ID) Unordered file -- > as the name suggests as the data in no particular order. Disadvantages of using sequential files

Back to Contents Back to Contents Disadvantages of a Sequential File 1.You can only add a new record at the end of the file 2.If a record needs to be replaced it must be the EXACT same length as the original 3.A record can only be updated if the data item used to replace the existing data is the same length as the original. 4.Processing of a sequential file is slower compared to other files. How?

Back to Contents Back to Contents How do you process records? You need to read through each and every record until you get the one you want. Only recommended for applications where most/all the records are to be processed at one time. For example: British Gas sends out bills to all their customers. You receive a bill after every three months. So a person who joins in January will receive their bill in April along with all the other people who also joined in January.

Back to Contents Back to Contents Functions in a Sequential File  Adding records -- > easy  Amending + Deleting -- > not so easy.  If it is an unordered sequential file  amending and deleting are fairly difficult  If it is an ordered sequential file  amending and deleting are sort of easy. This is done with the assistance of a transaction file. What is a transaction file? It contains the actions to be carried out on the records.

Back to Contents Back to Contents Performing Functions in an Ordered File The key field is used. Master File IDNameGender 1Mr AhmedMale 2Mrs RussellFemale 3Mr RoyaleMale 4Mr O’NeilMale Transaction File IDTrans.NameGender 1DMr AhmedMale 2CMr RussellMale 3DMr RoyaleMale 5AHafizMale New Master File IDNameGender 2Mr RussellMale 4Mr O’NeilMale 5HafizMale Computer reads the first record from the transaction and the master file. If the ID doesn’t match (In this case it does), the computer writes it to the new master file The next record is then read and the transaction is carried out by the computer D: Delete C: Change A: Add D: Delete C: Change A: Add

Back to Contents Back to Contents Indexed Sequential and Random Access Files These are stored in order As opposed to the sequential files that were stored on magnetic tape, index sequential are stored on a disk, allowing them to have direct access. Each record has a fixed field length. Having things ordered provides a greater speed of access.

Back to Contents Back to Contents Indexed Sequential and Random Access Files Indexed sequential -- > records are in an order (for example: by surname) Index: pointer to where on the disk the record is stored. The table may be from A-Z, the index can then point out where all the A’s are, where all the B’s are, etc. it works like the index of a book. If you search for something starting with ‘S’. All the records from A to R will be ignored. Then every record in the ‘S’ section is read one by one until what you get what you need.

Back to Contents Back to Contents Indexed Sequential and Random Access Files Banks use sequential access systems in order to process cheques. This will be very useful especially in online banking. Index sequential files are used with hybrid batch processing systems- employee records. This allows for direct access when an individuals record needs to be seen. Records held sequentially allowing serial access when producing a payroll.

Back to Contents Back to Contents Indexed Sequential and Random Access Files Random Access -- > quickest form of access. Despite the position of the desired record, it will take the same amount of time to access it. Each record has a key; the computer looks up the key -- > goes to the appropriate place on the disk to access it.

Back to Contents Back to Contents Hierarchical Database Management Systems (DMS) No longer used. Why? One-way relationship problem! A hierarchical DMS -- > family tree like structure. One mother can have many children, but the children can have only one mother.’ Windows system  several users  each user will have several documents Enabling fast access to data

Back to Contents Back to Contents Network Database Management System (DMS) Overcome the faults of the hierarchical DMS Many organisations now use a distributed database system. Data is stored on computers that are then linked by a LAN/WAN. Data in the database is duplicated several times, so it is unlikely to loose the data and it also gives the users faster access times. To a user it seems to be a single system

Back to Contents Back to Contents Network Database Management System (DMS) System caters for complex searches; search is not necessarily done at the site where the user is. For example: something that is done in Dukhan on our computers could be then processed in Doha.

Back to Contents Back to Contents Network Database Management System (DMS) Another type of Network DB  stored on one device– accessed from a number of network locations. Users access the database – but don’t slow the system down. For example: PNC (Police National Computer) and DVLA (Driver and Vehicle Licensing Authority)

Back to Contents Back to Contents Relational Database Systems What is a relational database? It consists of separate tables that are all related in some way. So this means that each table needs to have a key field that is a field in another table. So what? The data from the initial table can then be combined with data from another table when you need to produce reports.

Back to Contents Back to Contents Relational Database Systems Customer Customer ID Name: Date of Birth: Address: Telephone Number: DVD DVD ID Name of DVD: Number of Copies: Main Actor: Customer ID In this table the Customer ID is the Key Field In this table the DVD ID is the primary key. The Customer ID is the foreign key. These two tables are linked by the Customer ID.

Back to Contents Back to Contents Relational Database Systems Standard Programming Language dealing with relational tables is called Structured Query Language (SQL). What is it used for? It is used for queries and producing reports. Advantages of relational databases

Back to Contents Back to Contents Advantages of Relational Databases 1.Data not repeated – storage capacity not wasted. Comparing this to a flat file database, in which data is repeated. 2.Data retrieval is quicker. If the data is repeated, hackers will have greater ease in accessing the data. Relational databases reduce this risk. 3.They also allow room for expansion