General issues with interfaces

• Standardized interfaces
  Many interfaces are intended for reuse by many applications. Therefore, they separate their functionality into two groups.
  • Information regarding the reusable aspects of the interface (i.e., connections, sessions, supported units of transfer (files, whole records, etc.)).
  • Application-specific information (i.e., record layouts of tabular text files, the set of files, specific objects instances).

• Data resolution
  Division of application data encoding in up to two levels
  • Addressable by the interface (i.e., files via FTP, record column values via ODBC)
  • Not addressable by the interface (i.e., the FTP interface to retrieve an XML file, but FTP doesn't provide specific element extraction from that XML file.)

  Applications may have some freedom about where to encode information. For example, a FTP server for image files could serve one file per image (with a helpful filename), or could serve just one .zip file which must be opened by the client to choose the desired image file.

• Data types
  • Interface basic data types may or may not correspond well to the basic data types used to describe data at the data source.
  • Example In HTTP, all data is represented as a string. This works great for web pages. But if HTTP is being used to transfer a sound file, the string data type isn't particularly useful.
• Interface semantics
  • Data sources and data integrators are capable of encoding whatever information they choose in terms of an interface.
  • Some interface designs help provide hints to the semantics of application data moved across the interface. (I.e., ODBC allows its users to refer to specific table name, and those names might provide helpful hints as to the application semantics of the table contents.)
  • Why different interfaces suit different application data models Some interfaces are designed in a way that allows for obvious mapping between application data models and the interface. (I.e., ODBC with a relational database, or CORBA with an object-oriented system.)
  • Dealing with semantics of the application-specific data is covered in a another section (needs an xref)