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Tuple-versioning (also called point-in-time) is a mechanism used in a relational database management system to store past states of a relation. Normally, only the current state is captured.
A relational database management system (RDBMS) is a database management system (DBMS) based on the relational model of data. Most databases in widespread use today are based on this model.
In relational database theory, a relation, as originally defined by E. F. Codd, is a set of tuples (d1, d2, ..., dn), where each element dj is a member of Dj, a data domain. Codd's original definition notwithstanding, and contrary to the usual definition in mathematics, there is no ordering to the elements of the tuples of a relation. Instead, each element is termed an attribute value. An attribute is a name paired with a domain. An attribute value is an attribute name paired with an element of that attribute's domain, and a tuple is a set of attribute values in which no two distinct elements have the same name. Thus, in some accounts, a tuple is described as a function, mapping names to values.
Using tuple-versioning techniques, typically two values for time are stored along with each tuple: a start time and an end time. These two values indicate the validity of the rest of the values in the tuple.
In mathematics, a tuple is a finite ordered list (sequence) of elements. An n-tuple is a sequence of n elements, where n is a non-negative integer. There is only one 0-tuple, an empty sequence, or empty tuple, as it is referred to. An n-tuple is defined inductively using the construction of an ordered pair.
Typically when tuple-versioning techniques are used, the current tuple has a valid start time, but a null value for end time. Therefore, it is easy and efficient to obtain the current values for all tuples by querying for the null end time.
The null character is a control character with the value zero. It is present in many character sets, including ISO/IEC 646, the C0 control code, the Universal Coded Character Set, and EBCDIC. It is available in nearly all mainstream programming languages. It is often abbreviated as NUL.
A single query that searches for tuples with start time less than, and end time greater than, a given time (where null end time is treated as a value greater than the given time) will give as a result the valid tuples at the given time.
For example, if a person's job changes from Engineer to Manager, there would be two tuples in an Employee table, one with the value Engineer for job and the other with the value Manager for job. The end time for the Engineer tuple would be equal to the start time for the Manager tuple.
A table is an arrangement of data in rows and columns, or possibly in a more complex structure. Tables are widely used in communication, research, and data analysis. Tables appear in print media, handwritten notes, computer software, architectural ornamentation, traffic signs, and many other places. The precise conventions and terminology for describing tables vary depending on the context. Further, tables differ significantly in variety, structure, flexibility, notation, representation and use. In books and technical articles, tables are typically presented apart from the main text in numbered and captioned floating blocks.
The pattern known as log trigger uses this technique to automatically store historical information of a table in a database.
In relational databases, the Log trigger or History trigger is a mechanism for automatic recording of information about changes inserting or/and updating or/and deleting rows in a database table.
A table is a collection of related data held in a table format within a database. It consists of columns, and rows.
