Database Assignment Example | Topics and Well Written Essays - 1500 words

Database - Assignment Example The second layer is diversely treated by database modeling languages. Nevertheless, there are common features, especially type constructors. A common approach in most models is the generic definition of operations according to the structure of the type. The inductive specification of structuring is based on base types and type constructors. A type constructor is a function from types to a new type. The constructor can be supplemented with a selector for retrieval (like Select) with a retrieval expression and update functions (like Insert, Delete, and Update) for value mapping from the new type to the component types or to the new type, with correctness criteria and rules for validation, with default rules; current date for data assignment, with one or several user representations, and with a physical representation or properties of the physical representation. A base type is an algebraic structure B = (Dom(B); Op(B); Pred(B)) with a name, aSet of values in a domain, a set of operatio ns and a set of predicates. A class BC on the base type is a collection of elements from Dom (B). Usually, BC is required to be a set (DIETRICH, 2011). It can be also a list (denoted by ) multi-set ({|.|}), tree etc. Classes may be changed by applying operations. Elements of a class may be classified by the predicates. The value set can be discrete or continuous, finite or infinite. We typically assume discrete value sets. Typical predicates are comparison predicates such as ; Â ·; 6=; ?; =. Typical functions are arithmetic functions such as, - and x. The set of integers is given by the Integer Set. The base type is extended to a data type by explicit definition of properties of the under-lying value sets. Precision and accuracy; data can be precise to a certain extent. Precision is the degree of refinement in the calculations. Accuracy is a measure of how repeatable the assignment of values for properties is. Granularity: Scales can be fine or coarse. The accuracy of data depends on the granularity of the domain which has been chosen for the representation of properties. Ordering: The ordering of values of a given domain can be based on ordering schemes such as lexicographic, geographic or chronological ordering or on exact ordering such as orderings on natural numbers. The ordering can also be based on ontologies or categories. Scales have a range with lowest values and highest values. These values can be finite or infinite, if they are finite then overflow or underflow errors might be the result of a computation. Classification: The data can be used for representation of classifications; the classification can be linear, hierarchical, etc. The classification can be mono-hierarchical or poly-hierarchical, mono-dimensional, poly-dimensional, analytical, synthetically or even monothetic. The classification can be based on ontologies and can be maintained with thesauri. Presentation: The data type can be mapped to different representation types dependent on se veral parameters. For instance, in Web applications, the format chosen for presentation types of pictures depends on the capacity of the channel, on the compression etc. The presentation might be linear or hierarchical, and it can be layered. Implementation: The implementation the attribute type depends on the properties of the DBMS. The implementatio