After studying this chapter, you should be able to: Describe the basic concepts of files and file systems, understand the principal techniques for file organization and access, define B-trees, explain file directories, understand the requirements for file sharing. | Chapter 12 File Management Overview File organisation and Access File Directories File Sharing Record Blocking Files Files are the central element to most applications file as an input to applications file as an output for long-term storage and for later access Desirable properties of files: Long-term existence Controlled sharing between processes Structure that is convenient for particular applications File Structure Fields and Records Fields Basic element of data ., student’s last name Contains a single value Characterized by its length and data type Records Collection of related fields ., a student record Treated as a unit File Structure File and Database File Collection of similar records Treated as a single entity and may be referenced by name Access control restrictions usually apply at the file level Database Collection of related data Explicit relationships exist among elements Consists of one or more files A Big Picture How to identify and locate a . | Chapter 12 File Management Overview File organisation and Access File Directories File Sharing Record Blocking Files Files are the central element to most applications file as an input to applications file as an output for long-term storage and for later access Desirable properties of files: Long-term existence Controlled sharing between processes Structure that is convenient for particular applications File Structure Fields and Records Fields Basic element of data ., student’s last name Contains a single value Characterized by its length and data type Records Collection of related fields ., a student record Treated as a unit File Structure File and Database File Collection of similar records Treated as a single entity and may be referenced by name Access control restrictions usually apply at the file level Database Collection of related data Explicit relationships exist among elements Consists of one or more files A Big Picture How to identify and locate a selected file? How to enforce user access control in shared systems? How to organize records as a sequence of blocks for I/O? individual block I/O requests must be scheduled for optimizing performance How to organize records in a file and access a particular record in a file? Roadmap Overview File organisation and Access File Directories File Sharing Record Blocking File Organization The basic operations that a user or application may perform on a file are performed at the record level The file is viewed as having some structure that organizes the records File organization refers to the logical structuring of records Determined by the way in which files are accessed (access method) Criteria for File Organization Important criteria include: Short access time Ease of update Economy of storage Simple maintenance Reliability Criteria for File Organization Priority will differ depending on the use For batch mode file processing, rapid access for retrieval of a single record is of .
