Chapter 10 Databases

ion Abstraction is a key principle in every area of computer science – shielding people or programs that make use of a particular software artifact from knowing details that are “internal”. In the database context, this means that users of database systems should be shielded from the internals of database management – what data structures or algorithms are utilized to make access more efficient. Thus a user should be able to define only the structure of the data, without any information about concrete physical storage. The interface which describes the structure is a data definition language. Access to the data should only refer to the structure given in the definition. While standard programming languages provide a rich variety of data structures that can be defined by a user, relational languages require the user to describe data in terms of a very simple table data structure: a collection of attributes, each having values in some scalar datatype. The attributes of a table are unordered, allowing the data to be returned with any ordering of columns in addition to any ordering of rows. Fig. 10.1 Example database for the university enrollment setting 176 M. Benedikt and P. Senellartion is a key principle in every area of computer science – shielding people or programs that make use of a particular software artifact from knowing details that are “internal”. In the database context, this means that users of database systems should be shielded from the internals of database management – what data structures or algorithms are utilized to make access more efficient. Thus a user should be able to define only the structure of the data, without any information about concrete physical storage. The interface which describes the structure is a data definition language. Access to the data should only refer to the structure given in the definition. While standard programming languages provide a rich variety of data structures that can be defined by a user, relational languages require the user to describe data in terms of a very simple table data structure: a collection of attributes, each having values in some scalar datatype. The attributes of a table are unordered, allowing the data to be returned with any ordering of columns in addition to any ordering of rows. Fig. 10.1 Example database for the university enrollment setting 176 M. Benedikt and P. Senellart