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Semantic technologies for the Internet of Things

Payam Barnaghi

Institute for Communication Systems (ICS)

University of Surrey

Guildford, United Kingdom

International “IoT 360″ Summer SchoolOctober 29th – November 1st, 2014 – Rome, Italy

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Things, Data, and lots of it

image courtesy: Smarter Data - I.03_C by Gwen Vanhee

Data in the IoT

− Data is collected by sensory devices and also crowd sensing sources.

− It is time and location dependent.− It can be noisy and the quality can vary. − It is often continuous - streaming data.

− There are other important issues such as:− Device/network management− Actuation and feedback (command and control)

− Service and entity descriptions are also important.

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“Raw data is both an oxymoron and bad data”

Geoff Bowker, 2005

Source: Kate Crawford, "Algorithmic Illusions: Hidden Biases of Big Data", Strata 2013.

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From data to actionable information

Data

Information

Knowledge

Wisdom?

Raw sensory data

Structured data (with semantics)

Abstractions and perceptions

Actionable information

Heterogeneity, multi-modality and volume are among the key issues.

We need interoperable and machine-interpretable solutions…

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Semantics and Data

− Data with semantic annotations− Provenance, quality of information− Interpretable formats− Links and interconnections− Background knowledge, domain information− Hypotheses, expert knowledge − Adaptable and context-aware solutions

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Interoperable and Semantically described Data is the

starting point to create an efficient set of Actions.

The goal is often to create actionable information.

Wireless Sensor (and Actuator) Networks

Sinknode Gateway

Core networke.g. Internet

Core networke.g. InternetGateway

End-userEnd-user

Computer servicesComputer services

- The networks typically run Low Power Devices- Consist of one or more sensors, could be different type of sensors (or actuators)- The networks typically run Low Power Devices- Consist of one or more sensors, could be different type of sensors (or actuators)

Operating Systems?

Services?

Protocols?Protocols?

In-node Data

Processing

Data Aggregation/

Fusion

Inference/Processing of IoT data

Interoperable/Machine-

interpretablerepresentations

Interoperable/Machine-

interpretableRepresentations?

“Web of Things”

Interoperable/Machine-

interpretablerepresentations

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What we are going to study

− The sensors (and in general “Things”) are increasingly being connected with Web infrastructure.

− This can be supported by embedded devices that directly support IP and web-based connection (e.g. 6LowPAN and CoAp) or devices that are connected via gateway components. − Broadening the IoT to the concept of “Web of Things”

− There are already standards such as Sensor Web Enablement (SWE) set developed by the Open Geospatial Consortium (OGC) that are widely being adopted in industry, government and academia.

− While such frameworks provide some interoperability, semantic technologies are increasingly seen as key enabler for integration of IoT data and broader Web information systems.

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Observation and measurement data- annotation

Tags

Data formats

Location

Source: Cosm.com

Observation and measurement data

15, C, 08:15, 51.243057, -0.589444

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value

Unit of measurement

Time

Longitude

Latitude

How to make the data representations more machine-readable and machine-interpretable;

Observation and measurement data

15, C, 08:15, 51.243057, -0.589444

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<value>

<unit>

<Time>

<Longitude>

<Latitude>

What about this?

<value>15</value><unit>C</unit><time>08:15</time><longitude>51.243057</longitude><latitude>-0.58944</latitude>

Extensible Markup Language (XML)

− XML is a simple, flexible text format that is used for data representation and annotation.

− XML was originally designed for large-scale electronic publishing.

− XML plays a key role in the exchange of a wide variety of data on the Web and elsewhere.

− It is one of the most widely-used formats for sharing structured information.

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XML Document Example

<?xml version="1.0"?>

<measurement>

<value>15</value>

<unit>C</unit>

<time>08:15</time>

<longitude>51.243057</longitude>

<latitude>-0.58944</latitude>

</measurement>

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XML Prolog- the XML declaration

XML elements

XML documents MUST be “well

formed”

Root element

XML Document Example- with attributes

<?xml version="1.0“ encoding="ISO-8859-1"?>

<measurement>

<value type=“Decimal”>15</value>

<unit>C</unit>

<time>08:15</time>

<longitude>51.243057</longitude>

<latitude>-0.58944</latitude>

</measurement>

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Well Formed XML Documents

− A "Well Formed" XML document has correct XML syntax.

− XML documents must have a root element− XML elements must have a closing tag− XML tags are case sensitive− XML elements must be properly nested− XML attribute values must be quoted

17Source: W3C Schools, http://www.w3schools.com/

Validating XML Documents

− A "Valid" XML document is a "Well Formed" XML document, which conforms to the structure of the document defined in an XML Schema.

− XML Schema defines the structure and a list of defined elements for an XML document.

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XML Schema- example

<xs:element name=“measurement">

<xs:complexType>  <xs:sequence>    <xs:element name=“value" type="xs:decimal"/>    <xs:element name=“unit" type="xs:string"/>    <xs:element name=“time" type="xs:time"/>    <xs:element name=“longitude" type="xs:double"/>

<xs:element name=“latitude" type="xs:double"/>  </xs:sequence></xs:complexType>

</xs:element>

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- XML Schema defines the structure and elements- An XML document then becomes an instantiation of the document defined

by the schema;

XML Documents– revisiting the example

<?xml version="1.0"?>

<measurement>

<value>15</value>

<unit>C</unit>

<time>08:15</time>

<longitude>51.243057</longitude>

<latitude>-0.58944</latitude>

</measurement>

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<?xml version="1.0"?> “But what about this?”

<sensor_data>

<reading>15</reading>

<u>C</u>

<timestamp>08:15</timestamp>

<long>51.243057</long>

<lat>-0.58944</lat>

</sensor_data>

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XML

− Meaning of XML-Documents is intuitively clear− due to "semantic" Mark-Up− tags are domain-terms

− But, computers do not have intuition− tag-names do not provide semantics for machines.

− DTDs or XML Schema specify the structure of documents, not the meaning of the document contents

− XML lacks a semantic model− has only a "surface model”, i.e. tree

Source: Semantic Web, John Davies, BT, 2003.

XML: limitations for semantic markup

− XML representation makes no commitment on:− Domain specific ontological vocabulary

− Which words shall we use to describe a given set of concepts?

− Ontological modelling primitives− How can we combine these concepts, e.g. “car is a-kind-of

(subclass-of) vehicle”

requires pre-arranged agreement on vocabulary and primitives

Only feasible for closed collaboration agents in a small & stable community pages on a small & stable intranet

.. not for sharable Web-resources

Source: Semantic Web, John Davies, BT, 2003. 22

Semantic Web technologies

− XML provide a metadata format.− It defines the elements but does not provide

any modelling primitive nor describes the meaningful relations between different elements.

− Using semantic technologies to solve these issues.

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A bit of history

− “The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in co-operation.“ (Tim Berners-Lee et al, 2001)

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Image source: Miller 2004

Semantics & the IoT

− The Semantic Sensor (&Actuator) Web is an extension of the current Web/Internet in which information is given well-defined meaning, better enabling objects, devices and people to work in co-operation and to also enable autonomous interactions between devices and/or objects.

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Resource Description Framework (RDF)

− A W3C standard− Relationships between documents− Consisting of triples or sentences:

− <subject, property, object>− <“Sensor”, hasType, “Temperature”>− <“Node01”, hasLocation, “Room_BA_01” >

− RDFS extends RDF with standard “ontology vocabulary”:− Class, Property− Type, subClassOf− domain, range

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RDF for semantic annotation

− RDF provides metadata about resources− Object -> Attribute-> Value triples or− Object -> Property-> Subject− It can be represented in XML − The RDF triples form a graph

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RDF Graph

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xsd:decimal

Measurement

hasValuehasTime

xsd:double

xsd:time

xsd:double

xsd:string

hasLongitude hasLatitude

hasUnit

RDF Graph- an instance

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15

Measurement#0001

hasValuehasTime

-0.589444

08:15

51.243057

C

hasLongitude hasLatitude

hasUnit

RDF/XML

<rdf:RDF>

<rdf:Description rdf:about=“Measurment#0001">

<hasValue>15</hasValue>

<hasUnit>C</hasUnit>

<hasTime>08:15</hasTime>

<hasLongitude>51.243057</hasLongitude>

<hasLatitude>-0.589444</hasLatitude>

</rdf:Description>

</rdf:RDF>

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Let’s add a bit more structure (complexity?)

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xsd:decimal

Location

hasValue

hasTime

xsd:double

xsd:time

xsd:double

xsd:string

hasLongitude

hasLatitude

hasUnit

Measurement

hasLocation

An instance of our model

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15

Location#0126

hasValue

hasTime

51.243057

08:15

-0.589444

C

hasLongitude

hasLatitude

hasUnit

Measurement#0001

hasLocation

RDF: Basic Ideas

−Resources−Every resource has a URI (Universal Resource

Identifier)−A URI can be a URL (a web address) or a some

other kind of identifier;−An identifier does not necessarily enable

access to a resources−We can think of a resources as an object that

we want to describe it.−Car−Person−Places, etc.

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RDF: Basic Ideas

− Properties− Properties are special kind of resources;− Properties describe relations between resources.− For example: “hasLocation”, “hasType”, “hasID”, “sratTime

”, “deviceID”,.− Properties in RDF are also identified by URIs.− This provides a global, unique naming scheme.− For example:

− “hasLocation” can be defined as:− URI: http://www.loanr.it/ontologies/DUL.owl#hasLocation

− SPARQL is a query language for the RDF data. − SPARQL provide capabilities to query RDF graph patterns

along with their conjunctions and disjunctions.

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Ontologies

− The term ontology is originated from philosophy. In that context it is used as the name of a subfield of philosophy, namely, the study of the nature of existence.

− In the Semantic Web:− An ontology is a formal specification of a domain;

concepts in a domain and relationships between the concepts (and some logical restrictions).

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Ontologies and Semantic Web

− In general, an ontology describes a set of concepts in a domain.

− An ontology consists of a finite list of terms and the relationships between the terms.

− The terms denote important concepts (classes of objects) of the domain.

− For example, in a university setting, staff members, students, courses, modules, lecture theatres, and schools are some important concepts.

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Web Ontology Language (OWL)

− RDF(S) is useful to describe the concepts and their relationships, but does not solve all possible requirements

− Complex applications may want more possibilities:− similarity and/or differences of terms (properties or classes)− construct classes, not just name them− can a program reason about some terms? e.g.:

− each «Sensor» resource «A» has at least one «hasLocation»− each «Sensor» resource «A» has maximum one ID

− This lead to the development of Web Ontology Language or OWL.

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OWL

− OWL provide more concepts to express meaning and semantics than XML and RDF(S)

− OWL provides more constructs for stating logical expressions such as: Equality, Property Characteristics, Property Restrictions, Restricted Cardinality, Class Intersection, Annotation Properties, Versioning, etc.

Source: http://www.w3.org/TR/owl-features/ 38

Ontology engineering

− An ontology: classes and properties (also referred to as schema ontology)

− Knowledge base: a set of individual instances of classes and their relationships

− Steps for developing an ontology:− defining classes in the ontology and arranging the

classes in a taxonomic (subclass–superclass) hierarchy− defining properties and describing allowed values and

restriction for these properties− Adding instances and individuals

Basic rules for designing ontologies

− There is no one correct way to model a domain; there are always possible alternatives. − The best solution almost always depends on the

application that you have in mind and the required scope and details.

− Ontology development is an iterative process. − The ontologies provide a sharable and extensible form to

represent a domain model.

− Concepts that you choose in an ontology should be close to physical or logical objects and relationships in your domain of interest (using meaningful nouns and verbs).

A simple methodology

1. Determine the domain and scope of the model that you want to design your ontology.2. Consider reusing existing concepts/ontologies; this will help to increase the interoperability of your ontology. 3. Enumerate important terms in the ontology; this will determine what are the key concepts that need to be defined in an ontology. 4. Define the classes and the class hierarchy; decide on the classes and the parent/child relationships5. Define the properties of classes; define the properties that relate the classes; 6. Define features of the properties; if you are going to add restriction or other OWL type restrictions/logical expressions. 7. Define/add instances

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Semantic technologies in the IoT

− Applying semantic technologies to IoT can support: − Interoperability− effective data access and integration− resource discovery − reasoning and processing of data− knowledge extraction (for automated decision making

and management)

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Data/Service description frameworks

− There are standards such as Sensor Web Enablement (SWE) set developed by the Open Geospatial Consortium that are widely being adopted in industry, government and academia.

− While such frameworks provide some interoperability, semantic technologies are increasingly seen as key enabler for integration of IoT data and broader Web information systems.

Revisiting goals of the Internet of Things

− A primary goal of interconnecting devices and collecting/processing data from them is to create situation awareness and enable applications, machines, and human users to better understand their surrounding environments.

− The understanding of a situation, or context, potentially enables services and applications to make intelligent decisions and to respond to the dynamics of their environments.

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Sensor Markup Language (SensorML)

Source: http://www.mitre.org/

The Sensor Model Language Encoding (SensorML) defines models and XML encoding to represent the geometric, dynamic, and observational characteristics of sensors and sensor systems.

The Sensor Model Language Encoding (SensorML) defines models and XML encoding to represent the geometric, dynamic, and observational characteristics of sensors and sensor systems.

Using semantics

− Find all available resources (which can provide data) and data related to “Room A” (which is an object in the linked data)?− What is “Room A”? What is its location? returns “location”

data− What type of data is available for “Room A” or that “location”?

(sensor types)

− Predefined Rules can be applied based on available data− (TempRoom_A > 80°C) AND (SmokeDetectedRoom_A position==TRUE)

FireEventRoom_A

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Semantic modelling

− Lightweight: experiences show that a lightweight ontology model that well balances expressiveness and inference complexity is more likely to be widely adopted and reused; also large number of IoT resources and huge amount of data need efficient processing

− Compatibility: an ontology needs to be consistent with those well designed, existing ontologies to ensure compatibility wherever possible.

− Modularity: modular approach to facilitate ontology evolution, extension and integration with external ontologies.

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Existing models- SSN Ontology

− W3C Semantic Sensor Network Incubator Group’s SSN ontology (mainly for sensors and sensor networks, platforms and systems).

http://www.w3.org/2005/Incubator/ssn/http://www.w3.org/2005/Incubator/ssn/

Stimulus-Sensor-Observation

- The SSO Ontology Design Pattern developed following the principle of minimal ontological commitments to make it reusable for a variety of application areas.-Introduces a minimal set of classes and relations centered around the notions of stimuli, sensor, and observations. -Defines stimuli as the (only) link to the physical environment.

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SSN Ontology Modules

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Basic Structure

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SSN Ontology

Ontology Link: http://www.w3.org/2005/Incubator/ssn/ssnx/ssn

M. Compton et al, "The SSN Ontology of the W3C Semantic Sensor Network Incubator Group", Journal of Web Semantics, 2012.

5353

W3C SSN Ontology

makes observations of this type

Where it is

What it measures

units

SSN-XG ontologies

SSN-XG annotations

SSN-XG Ontology Scope

What SSN does not model

− Sensor types and models− Networks: communication, topology− Representation of data and units of measurement

− Location, mobility or other dynamic behaviours− Control and actuation− ….

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Web of Things

− Integrating the real world data into the Web and providing Web-based interactions with the IoT resources is also often discussed under umbrella term of “Web of Things” (WoT).

− WoT data is not only large in scale and volume, but also continuous, with rich spatiotemporal dependency.

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Web of Things

Connecting sensor, actuator and other devices to the World Wide Web.

“Things’ data and capabilities are exposed as web data/services.

Enables an interoperable usage of IoT resources (e.g. sensors, devices, their data and capabilities) by enabling web based discovery, access, tasking, and alerting.

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Example: Linked IoT Data

Internal location ontology (local)

Lined-data location(external)

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The world of IoT and Semantics: Challenges and issues

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Some good existing models: SSN Ontology

Ontology Link: http://www.w3.org/2005/Incubator/ssn/ssnx/ssn

M. Compton et al, "The SSN Ontology of the W3C Semantic Sensor Network Incubator Group", Journal of Web Semantics, 2012.

Semantic Sensor Web

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“The semantic sensor Web enables interoperability and advanced analytics for situation awareness and other advanced applications from heterogeneous sensors.” (Amit Sheth et al, 2008)

Several ontologies and description models

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We have good models and description frameworks;

The problem is that having good models and developing ontologies is not enough.

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Semantic descriptions are intermediary solutions, not the end product.

They should be transparent to the end-user and probably to the data producer as well.

A WoT/IoT Framework

WSNWSN

WSNWSN

WSNWSN

WSNWSN

WSNWSN

Network-enabled DevicesNetwork-enabled Devices

Semantically annotate data

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GatewayCoAP

HTTP

CoAP

CoAP

HTTP

6LowPAN

Semantically annotate data

http://mynet1/snodeA23/readTemp?

WSNWSN

MQTT

MQTT

Gateway

And several other protocols and solutions…

Publishing Semantic annotations

− We need a model (ontology) – this is often the easy part for a single application.

− Interoperability between the models is a big issue. − Express-ability vs Complexity is a challenge

− How and where to add the semantics− Where to publish and store them− Semantic descriptions for data, streams, devices

(resources) and entities that are represented by the devices, and description of the services.

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Simplicity can be very useful…

Hyper/CAT

67Source: Toby Jaffey, HyperCat Consortium, http://www.hypercat.io/standard.html

- Servers provide catalogues of resources toclients.

- A catalogue is an array of URIs.

- Each resource in the catalogue is annotatedwith metadata (RDF-like triples).

Hyper/CAT model

68Source: Toby Jaffey, HyperCat Consortium, http://www.hypercat.io/standard.html

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Complex models are (sometimes) good for publishing research papers….

But they are often difficult to implement and use in real world products.

What happens afterwards is more important

− How to index and query the annotated data− How to make the publication suitable for constrained

environments and/or allow them to scale− How to query them (considering the fact that here we are

dealing with live data and often reducing the processing time and latency is crucial)

− Linking to other sources

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The IoT is a dynamic, online and rapidly changing world

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isPartOf

Annotation for the (Semantic) Web

Annotation for the IoT

Image sources: ABC Australia and 2dolphins.com

Make your model fairly simple and modular

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SSNO model

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Creating common vocabularies and taxonomies are also equally important e.g. event taxonomies.

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We should accept the fact that sometimes we do not need (full) semantic descriptions.

Think of the applications and use-cases before starting to annotate the data.

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Semantic descriptions can be fairly static on the Web;

In the IoT, the meaning of data and the annotations can change over time/space…

Static Semantics

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Dynamic Semantics

<iot:measurement><iot:type> temp</iot:type><iot:unit>Celsius</iot:unit><time>12:30:23UTC</time><iot:accuracy>80%</iot:accuracy><loc:long>51.2365<loc:lat><loc:lat>0.5703</loc:lat></iot:measurment>

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- But this could be also a function of time and location;

- What would be the accuracy 5 seconds after the measurement?

- Should it be a part of this model?

Dynamic annotations for data in the process chain

78S. Kolozali et al, A Knowledge-based Approach for Real-Time IoT Data Stream Annotation and Processing", iThings 2014, 2014.

Dynamic annotations for provenance data

79S. Kolozali et al, A Knowledge-based Approach for Real-Time IoT Data Stream Annotation and Processing", iThings 2014, 2014.

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Semantic descriptions can also be learned and created automatically.

Extraction of events and semantics from social media

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City Infrastructure

Tweets from a city

P. Anantharam, P. Barnaghi, K. Thirunarayan, A. Sheth, "Extracting city events from social streams,“, 2014.

https://osf.io/b4q2t/

Ontology learning from real world data

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Overall, we need semantic technologies in the IoT and these play a key role in providing interoperability.

However, we should design and use the semantics carefully andconsider the constraints and dynamicity of the IoT environments.

#1: Design for large-scale and provide tools and APIs.

#2: Think of who will use the semantics and how when you design your models.

#3: Provide means to update and change the semantic annotations.

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#4: Create tools for validation and interoperability testing.

#5: Create taxonomies and vocabularies.

#6: Of course you can always create a better model, but try to re-use existing ones as much as you can.

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#7: Link your data and descriptions to other existing resources.

#8: Define rules and/or best practices for providing the values for each attribute.

#9: Remember the widely used semantic descriptions on the Web are simple ones like FOAF.

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#10: Semantics are only one part of the solution and often not the end-product so the focus of the design should be on creating effective methods, tools and APIs to handle and process the semantics.

Query methods, machine learning, reasoning and data analysis techniques and methods should be able to effectively use these semantics.

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Data analytics framework

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Data:

DataData

Domain

KnowledgeDomain

Knowledge

Social

systemsSocial

systemsInteractionsInteractionsOpen

InterfacesOpen

Interfaces

Ambient

IntelligenceAmbient

IntelligenceQuality and

TrustQuality and

Trust

Privacy and

SecurityPrivacy and

Security

Open DataOpen Data

In summary

IoT data: semantic related issues

− The current IoT data communications often rely on binary or syntactic data models which lack of providing machine interpretable meanings to the data.

− Syntactic representation or in some cases XML-based data

− Often no general agreement on annotating the data

− requires a pre-agreement between different parties to be able to process and interpret the data

− Limited reasoning based on the content and context data

− Limited interoperability in data and resource/device description level

− Data integration and fusion issues

Requirements

− Structured representation of concepts

− Machine-interpretable descriptions

− Reasoning mechanisms

− Access mechanism to heterogeneous resource descriptions with diverse capabilities

− Automated interactions and horizontal integration with existing applications

What are the challenges?

− The models provide the basic description frameworks, but alignment between different models and frameworks are required.

− Semantics are the starting point, reasoning and interpretation of data is required for automated processes.

− Real interoperability happens when data/services from different frameworks and providers can be interchanged and used with minimised intervention.

Possible solutions?

− The semantic Web has faced this problem earlier. − Proposed solution: using machine-readable and machine-interpretable

meta-data− Important not: machine-interpretable but not machine-untreatable!− Well defined standards and description frameworks: RDF, OWL, SPARQL− Variety of open-source, commercial tools for creating/managing/querying and

accessing semantic data− Jena, Sesame, Protégé, …

− An Ontology defines conceptualisation of a domain.− Terms and concepts− A common vocabulary − Relationships between the concepts

− There are several existing and emerging ontologies in the IoT domain.− HyperCat model − W3C SSN ontology− And many more

− Automated annotation methods, dynamic semantics

How to adapt the solutions?

− Creating ontologies and defining data models are not enough− tools to create and annotate data− data handling components

− Complex models and ontologies look good, but− design lightweight versions for constrained environments − think of practical issues− make it as much as possible compatible and/or link it to the other

existing ontologies − Domain knowledge and instances

− Common terms and vocabularies − Location, unit of measurement, type, theme, …

− Link it to other resource − Linked-data− URIs and naming

− In many cases, semantic annotations and semantic processing should be intermediary not the end products.

What are the practical steps?

− Linked data approach is a promising way of integrating data from different sources and interlinking semantic descriptions;

− Alignment between different description models for Services/Resources/Entities;

− Using common models (e.g. HyperCat, SSNO) and developing applications and services that use these information represented based on the models;

− Ontology learning from real world data;

− Dynamic and automated annotations;

− Semantic processing, scalable (distributed) repository, discovery, query and analysis support;

− Tools and support for real-time and streaming (semantically annotated) data;

Quiz

− Design a simple ontology (model) to describe operating system and different sensors on a smart phone.

Q&A

− Payam Barnaghi, University of Surrey/EU FP7 CityPulse Project

http://www.ict-citypulse.eu/

@pbarnaghi

p.barnaghi@surrey.ac.uk