It concisely introduces fundamental temporal database concepts, surveys state-of-the-art solutions to challenging aspects of temporal data management, and also offers a look into the future of temporal database research. Most applications of database technology are temporal in nature. Examples include financial applications such as portfolio management, accounting, and banking; record-keeping applications such as personnel, medical-record, and inventory management; scheduling applications such as airline, train, and hotel reservations and project management; and scientific applications such as weather monitoring.
Applications such as these rely on temporal databases, which record time referenced data. The facts recorded by the database entities are of fundamental interest. Several different temporal aspects may be associated with these. Most importantly, the valid time of a fact is the collected times—possibly spanning the past, present, and future—when the fact is true in the mini-world. Valid time thus captures the time-varying states of the mini-world. All facts have a valid time by definition. However, the valid time of a fact may not necessarily be recorded in the database, for any of a number of reasons.
For example, the valid time may not be known, or recording it may not be relevant for the applications supported by the database. If a database models different possible worlds, the database facts may have several valid times, one for each such world. Next, the transaction time of a database fact is the time when the fact is current in the database. Unlike valid time, transaction time may be associated with any database entity, not only with facts. For example, transaction time may be associated with objects and values that are not facts because they cannot be true or false in isolation.
Relational Database Concepts and Applications: Research Paper
Introduction In order to successfully transition from our current paper and email based equipment request method to a completely paperless online system, we must build and implement a relational database. A relational database will allow us to store, filter, make changes to, and share of the data that is needed in our new online equipment ordering system. Relational Database Overview “Databases ...
To be more concrete, the value “63” may be stored in a database, but does not denote a logical statement. It is meaningful to associate transaction time with “63,” but not valid time. Thus, all database entities have a transaction-time aspect. This aspect may or may not, at the database designer’s discretion, be captured in the database. The transaction-time aspect of a database entity has duration: from insertion to deletion, with multiple insertions and deletions being possible for the same entity. As a consequence of the semantics of transaction time, capturing this aspect of database entities renders deletions purely logical.
Methods simply returning values, for example, calculating the age of a person from his birth date can be seen as dynamically calculated attribute values. This means that such methods could be treated like attribute values. However, time stamping methods with valid time and transaction time introduces problems if the methods have side effects. A method calling a program, for example, a WWW browser referring to a specific homepage, should only be allowed to be used if its valid time and/or transaction time overlaps time instant now, because this expresses that the method is both valid and stored in the database at the time instant it is called.
Otherwise, the method (meaning the access to the specific homepage) is either not valid anymore or it was deleted and thus should not be used. Third, this thesis focuses only on managing time-varying data. The data models introduced and proposed are specialist models since they are restricted to temporal data. However, instead of supporting specialist DBMS handling, for example, temporal or spatial database applications, an approach could be chosen which allows a system to be modified or extended such that special semantics of the application domain can be used for efficient data processing.
The Essay on The Entity Relationship Diagram
The Entity Relationship Diagram (ERD) depicts a conceptual data model that incorporates some of the important scientific information about the real world. It adopts a natural view that the real world consists of entities and relations (Chen, 1976). One objective of the ERD is to create a simple, easy to understand and conveniently presented data model consisting of entities, attributes, ...
