Ch 8 data base


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Ch 8 data base

  1. 1. 1 Chapter # 8 How Data is stored DATABASE
  2. 2. 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. 3. 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. 4. 4 Examples Roll No Name Phone# DOB 1 Ali 042-78888 12/12/98 2 Ahmed 544545 09/4/97 FIELD RECORD ITEM A Students Files
  5. 5. 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. 6. 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. 7. 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. 8. 8 Advantages of variable over fixed length • There is no waste of storage space • Advantages of fixed over variable 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. 9. 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. 10. 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. 11. 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. 12. 12 Transaction log files • Are bits of business such as placing an order, updating the stock, making a payment.
  13. 13. 13 File Access Methods • Serial access • Sequential access • Random Access
  14. 14. 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. 15. 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
  16. 16. 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. 17. 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. 18. 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. 19. 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. 20. 20 Files Systems • Manual File System • Mechanical File System • Electronic File Systems
  21. 21. 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. 22. 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. 23. 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. 24. 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. 25. 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. 26. 26 Data base • Database is organized collection of information or data. • Collection of related data stored in an efficient and compact manner.
  27. 27. 27 Examples • ATM • NADRA • Flight Details • Hotmail Or Yahoo Or Google • Library in Schools
  28. 28. 28 Types of Database • Centralized database • Distributed database
  29. 29. 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. 30. 30 Distributed database • Is a single database which is spread physically across multiple computers over wide area network . • It may be • Homogenous • Heterogeneous
  31. 31. 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. 32. 32 Database System of a School Students Data DBMS Admission program Schedule Program
  33. 33. 33 Common File processes • File updating • Insertions • Deletions • Amendments
  34. 34. 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. 35. 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. 36. 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. 37. 37 Amendments • Some changes occur in the field of file. • A pupil has moved house so the address field needs changing.
  38. 38. 38 File Manipulations • Sorting • Merging
  39. 39. 39 Sorting • Some time a field need to be sorted in particular order. • It may be • Ascending • Descending
  40. 40. 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.