File Management
- 1. FILE MANAGEMENT PRESENTED BY M.RAMYA. M.sc(CS & IT) NADAR SARASWATHI COLLEGE OF ARTS & SCIENCE. VADAPUDUPATTI , THENI.
- 2. FILE MANAGEMENT • A file management system is a type of software that manages data files in a computer system. • It has limited capabilities and is designed to manage individual or group files, such as special office documents and records. • It may display report details, like owner, creation date, state of completion and similar features useful in an office environment. • A file management system is also known as a file manage
- 3. FILES • Files are used for storing the Data of the users for a Long time Period. • The files can contains any type of information means they can Store the text, any Images or Pictures or any data in any Format. • So that there must be Some Mechanism those are used for Storing the information, Accessing the information and also Performing Some Operations on the files.
- 4. TYPES OF FILES • Field • Record • File • Database
- 5. • FIELD: A field is the basic element of data . An individual field contains a single value such as an employee’s last name, a date , or the values of a sensor reading . It is characterized by its length and data type. • RECORD: It is a collection of related fields that can be treated as a unit by some application programs. eg: An employee record would contains such fields as name , social security number , and soon.
- 6. • FILE: File is a collection of similar records . It is treated as a single entity by users and applications and may be referenced by name .files have unique file names and may be created and deleted. • DATABASE: It is a collection of related data . Database may contains all the information related to an organization or projects such as business or a scientific study .
- 7. FILE MANAGEMENT SYSTEM • A file management system is that set of system software that provides services to users and applications related to the use of files . A user are application may access files is through the file management system.
- 8. OBJECTIVES FOR THE FILE MANAGEMENT SYSTEM • Guarantees data in the file is valid . • Optimizes performs in terms of throughput and response time. • Provide I/O support for storage device type. • Provide I/O support for multiple users. • Minimize are eliminate the potential for lost or destroyed data. • Provide a standardized set of I/O interface routines. • Meet the data management needs and requirements for the user.
- 9. REQUIREMENTS • Each user should be able to create , delete and change files. • Each user may have controlled accesses to other users files. • Each user may control what types of accesses are allowed to the users files. • Each user should be able to restructure the users files in a form appropriated to the problem. • Each user should be able to move data between files. • Each user should be able to back up and recover the users files in case of damage. • Each user should be able to access the users files by a symbolic name.
- 10. FILE SYSTEM ARCHITECTURE • Different system will be organized differently , but this organization is reasonably representative. • At the lowest level , device drivers communicate directly with peripheral devices or their controllers are channels . A device driver is responsible for starting I/O operations on a device and processing the completion of an I/O request . In file operations, typical devices controlled are disk and tape drives . Devices drives are considered to be part of the operating system.
- 11. • The next level is referred to as the basic file system or the physical I/O level , which is the primary interface with the environment outside of the computer system . It deals with blocks of data that are exchanged with disk or tape systems. • The basic I/O supervisor is responsible for all file I/O initiation and termination . At this level , control structures are maintained that deal with device I/O , scheduling and file status . The basic I/O supervisor is concerned with the selection of the device on which file I/O is to be performed , on the basis of which file has been selected.
- 12. • Logical I/O is the part of the file system that allows users and applications to access records . Thus , where as the basic file system deals with blocks of data , the logical I/O module deals with file records . Logical I/O provides a general-purpose record I/O capability and maintains basic data about files. • Finally , the level of the file system closest the user is usually termed the access method . It provides a standard interface between applications and the file systems and devices that hold the data . Different access methods reflect different file structures and different ways of accessing and processing the data .
- 13. FILE ORGANIZATION AND ACCESS A file consists of a collection of records. In this section , we use the term file organization to refer to the logical structuring of the records as determined by the way in which they are accessed. Several criteria are important: • Rapid access for effective information retrieval. • Ease of update to aid in having up-to-date information. • Economy of storage to reduce storage costs. • Simple maintenance to reduce cost and potential for error. • Reliability to assure confidence in the data.
- 14. Most structure used in actual systems either fall into one of these categories or can be implemented with a combination of these organizations. The five organization are: • The pile • The sequential file • The indexed-sequential file • The indexed file • The direct , or hashed , file
- 15. THE PILE • The least complicated form of file organization may be termed the pile. • Each field should be self-describing , including a field name as well as value. • There is no structure to the pile file . pile files are perfectly adequate for exhaustive searches and are easy to update.
- 16. THE PILE Variable-length records Variable set of fields Chronological order
- 17. THE SEQUENTIAL FILE • The most common form of file structure is the sequential file. • In this type of file , a fixed format is used for records . All records are the same length , consisting of the same number of fields of fixed length in a particular order. • The sequential file organization is the only one that is easily stored on tape as well as on disk.
- 18. THE SEQUENTIAL FILE Fixed-length records Fixed set of fields in fixed order Sequential order based on key field
- 19. THE INDEXED SEQUENTIAL FILE • The most popular approach to overcoming the disadvantages of the sequential is the indexed sequential file. • The indexed provides a lookup capability to quickly reach the desired record. • Each record in the indexed file consists of two fields: a key field , which is the same as the key field in the main file and a pointer into the main file.
- 20. THE INDEXED SEQUENTIAL FILE
- 21. THE INDEXED FILE • The indexed sequential file retains one limitation of the sequential file . Effective processing is limited to that which is based on a single field of the file. • Two types of indexes are used. • An exhaustive index contains one entry for every record in the main file. • A partial index contains entries to records where the field of interest exists.
- 22. THE INDEXED FILE
- 23. THE DIRECT , OR HASHED , FILE • The direct , or hashed , file exploits the capability found on disks to directly access any block of a known address. • Direct file are often used where very rapid access is required , where records of fixed length are used and records are always access one at a time. • Example: directories , pricing tables , schedules and name lists.
- 24. FILE DIRECTORIES CONTENT: • File management system and collection of files is a file directory. • The directory contains information about the files , including attributes , location and ownership. • Virtually all system deal with different types of files and different file organizations and this information is also provided.
- 25. STRUCTURE: The requirements for a file structure , it is well to consider the types of operations that may be performed on the directory: • Search • Create file • Delete file • List directory
- 26. NAMING: • User needs to be refer to a file by a symbolic name . Each file in the system must have a unique name . • The path name /user B/word/unit A/ABC . The slash is used to delimit names the sequence. • The name of the master directory is implicit because all paths start that directory. • An interactive user or a process have associated with it a current directory , often referred to as the working directory.