Fig. 5.1 PEM components
services. This component relies on the SIM Web interface component to provide
information about sensing capacities of registered WSNs. For doing so, the SIM Web
interface component implements a functionality to send advertising messages con-
taining WSN metadata to PEM. A typical advertising message contains the network
identifier, types of sensing units in the network, geographic localization, network
creation time, RESTful Web Services provided by the network, among other rel-
evant information. These messages are sent whenever a new WSN is registered
within SIM, whenever new sensing capacities are deployed in a registered WSN,
or whenever SIM detects nonoperating networks, which are no longer part of the
infrastructure. After receiving an advertising message, the Publish and Discovery
component calls the Data Manager component to update the information about the
registered WSN capabilities.
The Data Manager component is responsible for managing all data structures
required by PEM.
The EMML Script Manager component provides mechanisms to create, interpret,
and execute Web mashups specified through EMML scripts. Mashup creation in
PEM follows the same model as defined in the EMML specification, described in
the next Section.
5.3.1 EMML Programming Model
The EMML language has a number of specific elements that allow the programming
of mashups scripts. These elements allow a developer to perform the invocation
and consumption of remote data, the processing and enrichment of these data, the
programming of the mashup control logic, and the use of databases to manage the
handling of such information. The EMML programming elements can be extended
using macros. The PEM's EMML script manager uses the macro functionality for
creating a domain-specific language (DSL) to facilitate the construction of physical
mashups based on information provided by WSN.