D. Cougar
Cougar [19] is also a database approach quite similar to
TinyDB developed at Cornell University. It also defines a high
level SQL-like declarative query language. In such a query
the FROM statement describes a node or a group of nodes
called Abstract Data Types (ADTs) whereas the SELECT and
WHERE statements refer to node specific data, invoking an
abstract method which includes attributes for the node like
input arguments, output values or timestamp. The query string
is translated into a relational algebra expression. Then an
optimizer combines all expressions from actual active queries
and builds up a query execution plan. At the end a command
injector distributes the commands into the sensor network
according to the execution plan. Another issue considered in
this project is about using adaptive query processing that adds statistics-gathering to regular query processing and piggybacks
small feedback data on results to long-running queries. The
effort of this is to reduce administration overhead for gathering
status information which is permanently necessary to address
the general problem of lacking absolute knowledge about the
global state of the network.