Temporal database

Description

A temporal database is a collection of transactions ordered by their timestamps. A sample temporal database generated from the set of items, I={a,b,c,d,e,f}, is shown in below table:

Types of temporal databases:

1. Regular temporal database: Uniform time gap exists between any two transactions.
2. Irregular temporal database: Non-uniform time gap exists between any two transactions.
   
   • Type-1 irregular temporal database: Every transaction will have a distinct timestamp.
   • Type-2 irregular temporal database: Multiple transactions can have a common timestamp.

Rules to create a temporal database

1. Since TID of a transaction implicitly represents the row number, this information can be ignored to save space.
2. The first column in the database must represent a timestamp.
3. The timestamp of the first transaction must always start from 1. The timestamps of remaining transactions follow thereafter. In other words, the timestamps in a temporal database must be relative to each other, rather than being absolute timestamps.
4. Irregular time gaps can exist between the transactions.
5. Multiple transactions can have a same timestamp. In other words, multiple transactions can occur at a particular timestamp. (Please note that some pattern mining algorithms, especially variants of ECLAT, may not work properly if multiple transactions share a common timestamp.)
6. All items in a transaction must be seperated with a separator.
7. The items in a temporal database can be integers or strings.
8. ‘ Tab space ’ is the default seperator. However, temporal databases can be constructed using other seperators, such as comma and space.

Format of a temporal database

timestamp<sep>item1<sep>item2<sep>...<sep>itemN

Examples

Regular temporal database: Uniform time gap exists between the transactions.

1   a   b   c
2   d   e
4   a   e   f
7   d   f   g

Irregular temporal database (Type-1): Non-uniform time gap exists between the transactions. More important, every transaction contains a unique timestamp.

1   a   b   c
2   d   e
4   a   e   f
7   d   f   g

Irregular temporal database (Type-2): Non-uniform time gap exists between the transactions. More important, multiple transactions can have same timestamps.

1   a   b   c
1   d   e
4   a   e   f
8   d   f   g