( ) 1 Chapter # 8 How Data is stored DATABASE

( ) 2 Items An item of data means the smallest piece of data that may be a single name or a single number. Field A field is a area of a record reserved for one particular type of data. Each field contain one or more data items.

( ) 3 Record Record is a group of related items of data which together can be treated as a unit. The records are similar to one another in the type of data. Files A file is organized collection of related records. In computing a file is usually on backing store.

( ) 4 Examples Roll No NamePhone#DOB 1Ali /12/98 2Ahmed /4/97 FIELD RECORD ITEM A Students Files

( ) 5 Reasons for using files In any situations requiring a permanent source of data. In computer when the main store is so small for amount of data being processed.

( ) 6 Key field A key field is field that may be used to search a file. It is always useful to have one field which is unique to a particular record. Admission form no of each student. With the library system, the key field would be the number given to the book

( ) 7 Fixed and variable length fields Fields may be of fixed or variable length. If the fields are of fixed length then a given field in a record has a set number of characters positions reserved for it. We specify how long each field is going to be when we set up the structure of a database If the fields are of variable length, the number of characters in each is not determined beforehand.

( ) 8 Advantages of variable over fixed length There is no waste of storage space Advantages of fixed over vaiable length Computer operations such as searching can be carried out quickly. Allocation of storage space is more straight forward Updating the file is much easier

( ) 9 Types of Files 1.Master file Is a file used as a reference for a particular computer application It may be updated when necessary It is the most complete and up-to date version of a file. If the master file is lost or damaged and it is only copy, the whole system will break down.

( ) 10 Transaction file Is a file of temporary data which has been prepared in order to carry out a processing operation with the data on a master file It is used to update master file. A transaction is a piece of a business. Transaction can occur in any order, so it is necessary to sort a transaction file into the same order as the master file

( ) 11 Backup or security files Backup copies of files are in kept in case the original file is damaged or lost or cannot be used The importance of master file, back up copies of it should be taken at regular intervals in case it is stolen, lost or corrupted. Looking after your disks is not enough you should always keep backup copies of all important data.

( ) 12 Transaction log files Are bits of business such as placing an order, updating the stock, making a payment.

( ) 13 File Access Methods Serial access Sequential access Random Access

( ) 14 Serial access To read a serial file,a computer has to read each record until it reaches the one required. The records do not follow each other in any particular order. So if another record needs to be added it can just be added to the end of the file.

( ) 15 Sequential Access Access to a file is sequential when records can only be written to or read from it in order one after another. So if just one record is required then method is slow but if all the records are required then it becomes fast Sequential files can be stored on Magnetic tape Magnetic disk

( ) 16 Direct or Random Access When any record can be accessed without having to access other records first It store data on direct access. You can access both sequential and random files directly

( ) 17 Advantages of direct access over sequential access Selected records can be accessed far more quickly from direct access files. Records can be accessed in any chosen order. Records do not have to be put into any particular order before the file is created

( ) 18 Advantages of Sequential access over direct access Sequential files can be stored on most media including magnetic tape,paper tape and punched card For the programmer ; it is usually easier to write programs to handle sequential files

( ) 19 Factors for choice of method How may records are to accessed. If the records are to be accessed singly or few then direct access is used. How large the file is. If a file is small the time delay in searching it is not important therefore a sequential file is acceptable. Sequential files is often suitable for batch applications. The type of storage medium being used. If magnetic tape is to used then files may have sequentail.

( ) 20 Files Systems Manual File System Mechanical File System Electronic File Systems

( ) 21 Manual File File is Processed manually without using any machine or tool. Problems: Accessing the same information in same of two people can not possible. If a file is placed in wrong place then finding it again can be problem Updating the file is difficult.

( ) 22 Mechanical File System File is processed by using different device like typewriters, mechanical printers. That method is faster and more accurate than manual file.

( ) 23 Electronic file File is processed through computers Files and set of instructions are given to the computer as input and computer automatically processed that file.

( ) 24 Advantages of computerized system Information is stored only once, since most database software allows you to access information from several files. Files can be linked together which means that if you update one of the files. Changing is in easy way Data loss is less chance Validations checks may be made on the data as it is being entered into database.

( ) 25 Disadvantages If the computer breaks down you are not able to access the details. It is easy to copy computer file so there is a need to protect sensitive data. Training is needed to use the system

( ) 26 Data base Database is organized collection of information or data. Collection of related data stored in an efficient and compact manner.

( ) 27 Examples ATM NADRA Flight Details Hotmail Or Yahoo Or Google Library in Schools

( ) 28 Types of Database Centralized database Distributed database

( ) 29 Centralized database Complete data is located at a single computer and all the users access this single database. Its an efficient way to access and update data. Used in computer network environment.

( ) 30 Distributed database Is a single database which is spread physically across multiple computers over wide area network. It may be Homogenous Heterogeneous

( ) 31 DBMS Database management system is computerized record keeping system. Is a collection of programs, which are used to define,create and maintain database.

( ) 32 Database System of a School Students Data DBMS Admission program Schedule Program

( ) 33 Common File processes File updating Insertions Deletions Amendments

( ) 34 File Updating Involves bringing a file up-to-date with any changes that have occurred. There are various process that can take place during updating.

( ) 35 Insertions A new entry in the file. Suppose we had a file containing the details of pupils in a school. A new pupil may have joined the school and so that pupil’s details will need to be added to the file.

( ) 36 Deletions A delete record in the file. A pupil could have moved to a new school so that the pupil’s detail will need to be removed from the file.

( ) 37 Amendments Some changes occur in the field of file. A pupil has moved house so the address field needs changing.

( ) 38 File Manipulations Sorting Merging

( ) 39 Sorting Some time a field need to be sorted in particular order. It may be Ascending Descending

( ) 40 Merging Sometimes we want to combine the contents of two files to form a single The process of combining the files is called merging. If the two files to be merged are on magnetic tape then we must sort the tapes into order before merging them. Merging is very important when we want to divide the work.