From Unordered Files to Indexing

1
From Unordered Files to Indexing

• CSC 402 File Management Techniques

2
Unordered Files

• Placed in file in the order inserted (appended
  only)
• Operations
• Insertion
• Deletion
• Search
• DB needs the file structure to support efficient
  access to records by content

3
Indexes To Access by Content

• Index
• Key-Reference pair
• Simple Index

Data file
address
4
Operations using an Index

• Search by key
• Update

Data file
address
5
Insert with a Simple Index
address
Data file
Insert Chicago the musical with key of 201
6
Result of Insert
Data file
address
7
Deletion Using a Simple Index
Data file
address
Delete key 150
8
Result of Deletion
Not reclaiming space
address
Data file
Reclaiming space
address
Data file
9
The Index File

• A File of SimpleIndex
• Normal File Operations
• When created vs opened?
• When read?
• When written?

10
Adjusted File API

• bool Create(filename)
• bool Open(filename)
• bool Close(filename)
• int Read(data, key)
• int Write(data, key)
• int Append(data)

11
Simple Indexed File Organization
12
Secondary Indexes

• Non-primary key accesses
• Not guaranteed to be unique

Primary index
Secondary index
240
29
13
Secondary Indexes with a Reference File
Points to record
Points to the head of list
14
Using the Secondary Indexes
Star index
Genre index