Networking Reference
In-Depth Information
it, including headers, URL, query parameters, etc. The ST part from the REST name
means State Transfer that is embedded in the request's content. No information from
the previous request is stored by the server. This principle is related to the scalability
of the system as if a server maintain information for each user, its performance is
affected in case of concurrent access [ 18 ].
TheREST emphasis on resources is described by the Resource-Oriented Architec-
ture (ROA) [ 19 ]. This means that resources are addressed using the standard descrip-
tion in the format of URIs, for instance: http://www.smartsensor.com/sensor1 . URIs
provide an unique identification to a resource, regardless of its type and representa-
tion. Thus, resources can be represented by means of various formats, such as Hyper-
Text Markup Language (HTML), eXtended Markup Language (XML), JavaScript
Object Notation (JSON), that are machine-readable and processable. REST offers a
subset of HTTP commands to access and manipulate resources: GET, PUT, POST,
DELETE. GET is used to retrieve information from a resource; POST is used to
add new information; PUT is used to update information, writing to a resource;
and DELETE is used to remove information. Thus, those standard Web operations
enable the communication between the resources and the Web. REST requires that
all resources (different physical devices) support this set of stateless methods to be
accessable via Web. In this way, objects are abstracted as Web services [ 24 ]. Things
conforming to the REST principles are called RESTful .
According to Zeng et al. [ 24 ], the use of the REST architecture in WoT is due
to its low complexity and its loosing-coupling stateless interactions. In fact, several
objects are resource-constrained devices and only a lightweight solution can be used
for integrating them to the Web [ 9 ]. Once the resources are available in the Web,
developers can create mashups , which are newWeb applications composed by various
elements, including virtual Web services and physical Web services provided by
objects [ 9 , 24 ]. As any Web 2.0 application, mashups are built based on a set of
technologies (Atom [ 1 ], for instance), that supports the development of simple and
highly interactive user interfaces. Mashups created by composing data and services
of physical devices with other Web resources are called physical mashups .They
focus on the reuse of real world objects with different applications [ 6 , 9 ].
2.2 Middleware for IoT
The abovementioned technologies enable the connectivity of the objects to the Inter-
net andmake themaccessible andmanageable. However, to create value-added appli-
cations, by combining the resources connected to the Internet, a high abstraction
level model needs to be used. Middleware platforms have been proposed [ 7 , 11 , 16 ,
17 , 21 ] with the goal of facilitating the development of applications supporting the
interoperability of interconnected devices, alleviating the programmer of the burden
of dealing with the specificities of physical devices and networking environment.
Through the use of middleware platforms, services may be provided on top of the
resources connected to the Web, to facilitate the fast combination of features in
 
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