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In-Depth Information
5.10
\The Model"
Throughout this and the previous section we have also implied that a model
of the development problem emerges. That model is, in fact, the hypertext{like
woven path along alternative and chosen identications, denitions, executions
and interpretations of results and plans.
Requirements Capture 11
Hence the decision support system for sustainable
development must itself, as the user \navigates" around alternatives, selects and
rejects choices, etc., build up a graph-like web of the paths taken, with nodes
and edges suitably labelled with references to data and functions, explanatory,
informal text that the systems elicits from the user, etc.
We will have more to say about this in section 7.3.
6 A Federated GIS+DIS: (GaD)
2
I
2
S
By a
federated geographic information system
we understand a GIS+DIS
whose main information, the spatial and (spatially related) census (and other)
data and operations over these may reside across a global (i.e. worldwide) net-
work of \ordinary", already established or future geographic information systems
\plus" demographic information systems. These latter GISs+DISs may repre-
sent their information each in their own way. From a practical point of view such
GISs+DISs may be managed on
APIC [26], ArcInfo [27], ArcView [28], ERMapper
[29], IDRISI [30], InterGraph [31], MapInfo [32], PopMap [33], Redatam [34]
,and
other platforms.
The problem to be dealt with in this section is to properly integrate the
concepts of geographic and demographic information systems (GISs, DISs) with
the resource representation notions of the previous section.
Hence we need take a look at GISs and DISs. These are aggregations spatially
and statistically (tabular) data. By `federation' we mean the further aggregation
of individual GISs and DISs | as they may have been created and are maintained
locally, around the world, each covering \separate" but eventually, increasingly
more related resources.
6.1
A First Narrative
To explain our notion of `federation' further we rst present a \picture", then
some narrative, and nally a formal model.
A Picture:
A
\picture is sometimes worth a thousand words".
Later we shall
claim that a formula is oftentimes worth a thousand pictures.
Yet even pictures need be explained: Squares with emanating arrows desig-
nate storage cells of type pointer. \Landscape" rectangles labelled `text' desig-
nate unstructured, textual data (ie. text which informally describes formatted
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