Global Positioning System Reference
In-Depth Information
Comparison
By mapping the array models to Array Algebra (Baumann and Holsten
2012), the following common properties and differences were established.
All four array models share the concept of arrays as functions over a domain.
But, typing is possible only within Array Algebra. Compared to AML, AQL
and RAM, Array Algebra allows not only non-negative but also negative
indices allowing hyperobjects to be located anywhere with respect to the
coordinate reference system. Array Algebra, AQL and RAM all have a
generic array generator. Only AML does not have such a constructor. Array
Algebra additionally introduces the sorting operator. With respect to the
relational embedding, RAM maps arrays to relations which are accessible
by SQL. AQL is embedded into the nested relational calculus and in the
case of AML, the relational embedding is not discussed (Marathe and Salem
1997; 1999). Contrarily, Array Algebra does not make any assumptions
about an embedding data model, it provides typed arrays as basis for an
array sub-model of some other data model. In fact, the rasdaman API and
implementation relies on the object-oriented model of the Object Database
Management Group (ODMG) standard (Catell and Cattell 2000), and the
fi rst implementation has been on the object-oriented DBMS, O
2
, while ports
to various relational systems have been added only later.
Array DBMS
Array DBMS provides fl exible, scalable storage and retrieval services
specifi cally for array data. As in practice, all facets of database design need
to be adapted for embedding array model into some overall data model,
either as an analogy to tables or an additional attribute type. There are
many open research questions, addressing storage management, query
language design and formalization, query optimization, parallelization and
distributed processing, and scalability issues in general. A sample array
manipulation query
15
is as below:
for
c
in (
OIL_SPILL_MONTEREY_BAY
)
return
encode (((
c
[
t
(22)] > 0) and (
c
[
t
(12)] = 0)), “
png
”)
Fast access is the prime task of the array storage manager. Traditional
database tuples and objects tend to fi t well into a single database page—a
unit of disk access on server, typically 4 KB, while array objects can easily
15
The demo is based on the Monterey Bay oil spill monitoring's image timeseries, to map
areas which are contaminated on day 22 and are not contaminated on the day 10 of the spill,
accessible over the Web, see: http://www.earthlook.org
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