File Organization and Access

• File organization and access relates to the use of records, fields, and files.
• A record contains related data items (possibly of different types) stored in fields and treated as a single entity for processing.
• A field contains a single data item, and many fields comprise a record.
• Each field has a name, and one field is the key field used to identify the record.
• A data file is a collection of records holding the same types of information about different objects or individuals.

File Characteristics

• Permanence (whether it is permanent or temporary).
• File organization (how records are organized on the storage device).
• Record access (how records are located).

Master and Transaction Files

• Many businesses and organizations regularly access, modify, and store large amounts of files.
• A master file is a permanent, up-to-date file that stores the main information, summary data, and key fields.
• Master files contain permanent data, such as employee personal data, payroll data, employee status, and job title.
• Master files contain less permanent data, such as hours worked and taxes deducted, updated regularly.
• A transaction file is a temporary file used to update the master file.
• The transaction file updates the master file with operations like add, update, and delete.
• Add puts a new record into the master file.
• Update changes the contents of an existing record or field.
• Delete removes a record from the master file.
• A change file or transaction log records all changes to the transaction file, which is essential for tracking transaction history.

Record Matching

• A primary key identifies the record you want to update or delete.
• The primary key is a unique field within the record. ie. StudentId
• Without a key field, you cannot delete or update records.
• To update or delete records, compare the primary key in the transaction record with the master file record.
• If there is a match in the primary key, you can update or delete the master file record.
• Record matching functions correctly if both files are ordered on the key field.
• Record matching cannot work if either file is unordered.

File Organization

• Files and records need to be organized for easy access and updates.
• A database is an organized collection of data.
• A file is an entire set of data.
• A record is a subset of data found in a file.
• A field is a piece of data contained in a record.

Ordering and Access Methods

• Sequential file ordering stores records in a logical order, such as by name, date, or size.
• Records are easier to understand when sorted sequentially, such as alphabetically.
• Serial file ordering is similar to sequential but records are stored in the order they are added, without any specific order.
• Serial ordering captures transactions as they occur and allows for easy checking of transaction history.
• Records in serial order may be reorganized into a sequential order after processing or backup.

Sequential Access

• Sequential access reads records one by one in the order they are stored until the target is reached.
• Sequential access is effective for accessing, viewing, and modifying records in large batches, although it can be slow.
• Serial access also reads records one by one in the order they are stored until the desired record is found.

Random File Ordering and Access

• Random file ordering, or direct access file ordering, stores files in any order.
• The compute maps/indexes all the records so it ca find them later
• It provides fast access to records.
• Random access, or direct access, allows you to access the desired record directly without going through others by using indices.
• Think of a one-dimensional array where each array element has an index number to mark its location.

Index Sequential File Ordering and Access

• Index sequential file ordering uses an indexed file to store records which are stored sequentially, with a set of indices.
• Records can be accessed via their index number.
• It combines sequential and random file ordering and is used when records need to:
• Be sorted in sequence
• Be quickly accessible
• Index sequential file ordering uses sequential and direct access to search for records.
• Sequential access is used to go through each record.
• Direct access is used to find a specific record.

Methods of ordering and access

• The way that records are stored and accessed depends on the types of record, what they are used for and even the form of storage.
• A bank may store data about its daily transactions using magnetic tape, therefore sequential access is used
• A school will have a record for each student, stored on a file, each student's record must be accessible to review or update information, but all records must be printed out at the end of each school year to allocate students to new classes, and would therefore benefit from direct and sequential file ordering, so index sequential file ordering and access is probably the best system to use.

Understand file organization with records, fields, and files. Learn about master vs transaction files. Explore file characteristics such as permanence, organization, and record access methods.