Databases Reference
In-Depth Information
and DreamWeaver
32)
allow users to drag and drop visual objects into blank windows
to realize WYSIWYG and interactive layout specification environment.
3.3
Visual Environments
Since visual aspects are important in the Web page design, it is natural to provide
visual environments to support this. As explained in Subsection 3.2, there are
many Web page authoring tools that can be used for the layout specification.
Some visual facilities can support the data integration specification. QBE
50)
and
its variations are widely used for visual queries to the relational data. Semistructured
data can be manipulated by visual facilities, too. DataGuide
25)
is an abstract
specification of semistructured data, and can be used as a QBE-like query language
for semistructured data. XML-GL
12)
is a graph-based query language for XML
documents. BBQ is a visual interface for XMAS query specification in MIX. An
example of visual data manipulation languages for hybrid data models is HQBE
26)
,
which makes it possible to manipulate relations and structured documents through
the visual interface.
Recently, some research groups are studying the visual support for both the
data integration and data layout specification in the Web structure construction
task. Tiramisu
6
) is a well-known system to support the Web structure construction
on heterogeneous information sources. The layout specification can be done with
visual Web page authoring tools which are familiar to users. However, data
integration specification is given by
the site schema,
and full visual support is not
attained. InfoWeaver/AQUA
37)
provides an integrated visual interface to both
specifications. It looks like a typical Web page authoring tool. Its feature is that
the system automatically derives the data integration specification and the layout
specification from users' instance-based drag-and-drop operations. So the Web
structure construction process is totally integrated.
3.4
Other Issues
There are lots of other important issues related to the Web structure construction
problem. This section overviews important issues and works which we have not
mentioned so far.
There are studies on effective and efficient management frameworks for the
Web structure construction. In this article, we have divided this task into the data
acquisition and the data layout. Ceri and others
14)
identify five perspectives of
dataintensive Web sites: sturcture, derivation, navigation, page composition, and
presentation. They provide tools to construct Web sites from those perspectives.
The query processing issue is another major concern. Florescu and others
21)
attack the problem of when to compute and materialize Web site's contents, and
propose optimization techniques exploiting the structure of the Web site. Labrinidis
an others
30)
compare several materialization policies based on an analytical cost
model and actual experiments on an implemented system.
