Whilst the theory requires that any duplicate rows
in the result are automatically removed, practical query languages
like SQL allow the user to choose between results with or without
duplicate rows. Although often described as 'set-based' or
'set-oriented' languages, they are strictly multiset-oriented. [back]
Although many purists might object, in practice
this requirement is often relaxed and most OO programming languages
allow a distinction between private (hidden) and
public (directly accessible) attributes. Some also support
intermediate levels of information hiding in which access to some
attributes and methods may be restricted to objects of particular
classes only. [back]
Middleware is so widely used as a marketing term to
describe anything between the client browser and the target
resource that it has long ceased to have any useful meaning. [back]
For a prototype system that delivers different
tourist information according to a user's location, device
capabilities and interests, see Ryan
2002. [back]