Time-constrained web services for industrial automation [Elektronische Ressource] / vorgelegt von Markus Mathes

Markus Mathes

Sujets

• Informatik

Informations

• Publié par: philipps-universitat_marburg
• Publié le: 01 janvier 2009
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 5 Mo

Extrait

Time-Constrained Web Services
for Industrial Automation
Dissertation
zur Erlangung des
Doktorgrades der Naturwissenschaften
(Dr. rer. nat.)
dem Fachbereich Mathematik und Informatik
der Philipps-Universität Marburg
vorgelegt von
Markus Mathes
geboren in Bad Brückenau
Marburg
2009Vom Fachbereich Mathematik und Informatik der
Philipps-Universität Marburg als Dissertation
am 01.07.2009 angenommen.
Erstgutachter: Prof. Dr. Bernd Freisleben
Zweitgutachter: Prof. Dr. Bernhard Seeger
Tag der mündlichen Prüfung: 09.07.2009Erklärung
Ich versichere, dass ich meine Dissertation
Time-Constrained Web Services for Industrial Automation
selbständig, ohne unerlaubte Hilfe angefertigt und mich dabei keiner anderen als
der von mir ausdrücklich bezeichneten Quellen und Hilfen bedient habe.
Die Dissertation wurde in der jetzigen oder einer ähnlichen Form noch bei keiner
anderen Hochschule eingereicht und hat noch keinen sonstigen Prüfungszwecken
gedient.
Marburg, denAcknowledgments
I would like to acknowledge the help of several people during the course of this
doctoral thesis.
First of all, I would like to thank my thesis supervisor Prof. Dr. Bernd Freisleben
for his permanent support during the course of this thesis.
I would also like to thank Prof. Dr. Helmut Dohmann for numerous inspiring
discussions about the subject of this thesis.
My thank also goes to the TiCS development team for helping to implement,
test, and improve the framework: Christoph Stoidner, Roland Schwarzkopf, Steffen
Heinzl, Tim Dörnemann, and Jochen Gärtner.
I dedicate this thesis to my parents: Ingrid and Hubert Mathes.
Both taught me that success comes along with hard work.
iiiAbstract
Service-oriented architectures based on web services have become the de facto stan-
dard for the design and implementation of distributed applications. Due to their
standardization, web services are widely adopted for inter-organizational commu-
nication, but their use for intra-organizational communication is challenging, espe-
cially within enterprises of the manufacturing domain. Business processes within
an industrial enterprise have to satisfy predefined time constraints. More precisely,
the manufacturing process has to guarantee real-time, i.e. predefined deadlines have
to be kept. Today’s industrial enterprises use specialized hard- and software at
the manufacturing layer—industrial PCs (IPCs) and programmable logic controllers
(PLCs)—that run under vendor-specific operating systems and are implemented us-
ing vendor-specific tools. This mixture of technologies of different vendors leads
to numerous breaks in the communication paradigm. The interconnection of these
technologies results in additional costs and is often quite error-prone.
This thesis investigates the seamless use of web services as a homogeneous com-
munication backbone throughout the overall industrial enterprise with a focus on the
manufacturing layer. The common layered organization of an industrial enterprise—
consistingofthebusinesslayer,theintermediatelayer,andthemanufacturinglayer—
is avoided by using web services as the communication backbone. The need for
real-time makes the use of web services in industrial automation challenging. Web
service standards (e.g. SOAP for the invocation and WSDL for the description of
web services) and technologies (e.g. available SOAP engines) have emerged from the
Internet domain where processing is based on a best-effort basis (time constraints
are of little or no interest).
The Time-Constrained Services (TiCS) framework presented in this thesis is a
technical foundation for using web services in time-constrained environments with a
specific focus on industrial automation. TiCS is a tool suite for the development,
deployment, publication, composition, and execution of web services with time con-
straints, especially real-time constraints. TiCS consists of several components to
ease the entire development process for automation engineers who are normally not
familiar with web service technologies. The main components of the TiCS framework
can be distinguished according to their functionality:
• permit access to the manufacturing layer using web services
• permit the composition of several web services to a value-added workflow that
iiiiv
represents a production process
• offer a mechanism to describe the time constraints of web services and work-
flows
• permit the efficient transmission of binary web service parameters
Toaccessthemanufacturinglayerusingwebservices, theTiCSframeworkoffersa
real-time SOAP engine for IPCs called SOAP4IPC and for PLCs called SOAP4PLC.
Both engines permit an evolutionary change to a web service based communication
backbone, since existing hardware can be used further.
Most real-world production processes consist of several steps. Due to this reason,
it is necessary to combine web services to a multi-step workflow. The TiCS Modeler
supportsanautomationengineertodefinesuchworkflowswithregardtotherequired
time constraints.
The WS-TemporalPolicy language permits the description of time constraints for
web services and entire workflows. Since time constraints may vary over time, e.g.
compareprocessingduringpeaktimeandoff-peaktime, WS-TemporalPolicypermits
the definition of a validity period for time constraints.
The protocol predominantly used for the invocation of web services is SOAP.
Since SOAP is based on XML, it is necessary to encode binary parameters, resulting
in a remarkable overhead. For an efficient parameter transmission—a fundamental
prerequisite to process a web service within a given deadline—the TiCS framework
contains a component called Flex-SwA.
Despite the fact that the technologies developed in this thesis focus on industrial
automation, they can also be used in related research areas where web services are
used as the communication technology.