Presentation on theme: "Topic 7: File Organization. Definitions database collection of related files file collection of related records record collection of related fields."— Presentation transcript:
Topic 7: File Organization
Definitions database collection of related files file collection of related records record collection of related fields (e.g. Name, Age) key field uniquely identifies a record (e.g. UserID)
Sequential File Organization Records in a file are stored sequentially (in order) by some key field 2480 Bob 2569 Alice 3020 Paul Originally designed to operate on magnetic tapes What happens when we try to add a new record?
Partially-Indexed Sequential Files File index (address) ~ index in a book Partially index all the records Key field has direct index to a section where record of interest is located 1. Sequential search for key field 2. Directly link to section of records 3. Sequential search for record of interest
Direct Access File Organization Record address is derived (calculated) from key field No need to search through an index Example: Record Address = UserID MOD 8 + SSN MOD 3 This math operation is called “key hashing” or “hashing”
Fixed-length vs. Variable-length Records Fixed-length each record is a set size can be used with direct file organization access based on math calculations, so size must be fixed in length Variable-length each record is a variable size can be used with sequential file organization access is all indexed, so size does not matter
Logical vs. Physical Organization of Data logical organization the abstract way that the computer program is able to access the data use of logical structures (e.g. linked lists) physical organization the actual physical structure of data in memory i.e. what the sequence of bits look like in memory