Constraint Handling Rules at

January 18, 2016 10:07 AM
Constraint Handling Rules (CHR) is both an effective concurrent declarative constraint-based programming language and a versatile computational formalism.

While conceptually simple, CHR is distinguished by a remarkable combination of desirable features:

  • a semantic foundation in classical and linear logic,
  • an efficient sequential and parallel execution model,
  • guaranteed properties like the anytime online algorithm properties,
  • powerful analysis methods for deciding essential program properties.

For example, the following rule computes prime numbers:

prime(X) \ prime(Y) <=> Y mod X == 0 | true.

It takes two prime candidates X and Y and removes Y if the number is a multiple of X. Given the integers from 2 to n, then after exhaustive application of the rule, only prime numbers up to n remain in the end.


This example and others can be tried online, e.g. at (choose example "primes" in the Playground pull-down menu).

Implementations and free downloads of CHR


Implementations and free downloads of CHR can be found in most Prolog systems, in Java, JavaScript and Haskell.


For a quick overview of CHR, look at the slides of the CHR keynote talk at RuleML 2015:

For more information, you may start at the CHR book webpage:

In 2016, the annual CHR workshop will take place as special track of the conference:

So, submit and see you,
Thom Fruehwirth

Call for Papers: The 10th International Web Rule Symposium

December 7, 2015 9:59 AM
will be held at Stony Brook University, from July 5 to July 8. Past events were held in Sardinia (IT, 2002), Hiroshima (JP, 2004), Galway (IR, 2005), Athens (USA, 2006), Orlando (2007, 2008), Las Vegas (2009), Washington DC (2010), Barcelona (2011), Ft. Lauderdale (2011), Montpellier (2012), Seattle (2013), Prague (2014) and Berlin (2015).

RuleML 2016 will host multiple special tracks, as well as hosting the 10th International Rule Challenge, and the 6th RuleML Doctoral Consortium and Industry.

Important Dates

Register Title and Abstract in Easychair March 11, 2016
Paper Submission: March 18, 2016
Author Notification May 4, 2016
Camera Ready May 18, 2016
Conference: 5-8 July, 2016
Theory and Practice of Logic Programming A selection of the best papers from all tracks will be invited to be revised and extended for the post-conference publication in

a Special Issue of Cambridge journal

Theory and Practice of Logic Programming.

Special topic tracks

Smart Contracts, Blockchain and Rules

Smart Contracts have emerged as means to digitize and (semi-)automatically enforce (legal) contracts, backed by technologies --- a set of recent technologies that appeared the first time in the context of the cryptocurrencies bitcoin, but are now being transitioned to different domains.

Due to the relevance of rules in Smart Contracts, it is natural that the emerging area of Smart Contracts finds a relevant venue for dissemination and that RuleML uses this opportunity to expand the applicability of rule technologies.

Constraint Handling Rules

This track will bring together practitioners, interested in the theory and applications of Constraint Handling Rules ( ), including abductive reasoning, multi-agent systems, natural language processing, compilation, scheduling, spatial-temporal reasoning, testing and verification, and type systems.

Topics (not limited to): Semantics, Analysis, Methodologies, Applications, Extensions, Related Approaches

Event Driven Architectures and Active Database Systems

This special track will bring together practitioners, interested in the theory and applications of active databases.

Topics (not limited to): Complex Event Processing ( ), Active Database systems, Semantic Complex Event Processing, Stream Reasoning, Event-driven and Rule-based Systems for the Internet of Things ( )

Legal Rules and Reasoning

This track will bring together practitioners, interested in the legal rules and reasoning. Legal rules are interpretations of one or more norms formalized using logical rules in the form of antecedent and consequent.

Topics (not limited to): Learning from legal texts, Modeling normative rules, Regulatory compliance by rules, Modeling legislation, XML, standards for documents, Legal ontology, Semantic Web in Legal Domain, Legal Open Data and Rules, Reasoning about normative rules, Normative rules extraction by natural language processing.

Rule- and Ontology-Based Data Access and Transformation

This track solicits contributions on theoretical and practical aspects of rule- and ontology-based data access and transformation.

Topics (not limited to): Logics and rule languages of particular interest to data access or transformation, Tractability and intractability results for rule- and ontology-based systems in the presence of large amounts of data, Interactions between rules and in the presence of large amounts of data, Rule- and ontology-based data integration, Rule and ontology-driven user interfaces for data access, Implementations of R&OBDA&T systems, Reports on applications and lessons learnt

Rule Induction and Learning Track

This track will bring together practitioners, interested in and other learning aspects of learning rules and reasoning.

Topics (not limited to): Inductive rule learning, Classification rules, Association rules, Learning rules for the semantic web, Preference rules, Rule-based recommender systems, Relational learning, Learning business rules, Descriptive rule learning, Predictive rule learning

There will be 2 Semantic Web Meetups:
  1. The Stony Brook Semantic Web Meetup: (coordinators: Erich Bremer and Jonas Almeida).
  2. The New York Semantic Web Meetup: (coordinators: Marco Neumann and Chris Welty).

Workshop on Semantics and Services

December 4, 2015 11:59 AM
SADI, OWL/RIF, and RuleML Sessions at the 6th Atlantic Workshop on Semantics and Services

The 6th Atlantic Workshop on Semantics and Services (AWoSS 2015), on Dec. 9, 2015, in Fredericton, New Brunswick, Canada, includes sessions discussing SADI, OWL/RIF, and RuleML topics. Information about these and the other sessions can be found on the AWoSS 2015 website. Background information about the RuleML talks "The Integrated PSOA RuleML for Interoperating SQL Relations and SPARQL Graphs" (Harold Boley) and "The PSOATransRun 1.0 System for Object-Relational Reasoning in RuleML" (Gen Zou) can be found on the PSOA RuleML page; about "Grailog KS Viz 2.0: Graph-Logic Knowledge Visualization by XML-Based Translation" (Leah Bidlake) on the Grailog page; and about "Translating FOL RuleML 1.01/XML to TPTP with XSLT 2.0" (Meng Luan) on the TPTP RuleML page. The systems described in these talks and pages are implemented as open-source projects. The contact for RuleML is Harold Boley. The contact for AWoSS 2015 is Weichang Du.

RuleML 2015 Report, Part 2

November 23, 2015 9:39 AM
Following up on our first report, in this second part we want to share some impressions from RuleML 2015 with the RuleML community as well as provide some additional material that arrived after the first part was written.

First of all, we are happy to be able to show the links of the joint keynote presentation by Michael Genesereth of Stanford University about "The Herbrand Manifesto: Thinking Inside the Box". The slides are now available and you can also watch the presentation here:



The preceding Blog articles Constraint Handling Rules - What Else? and When Processes Rule Events link to the slides of the other keynote and the invited talk. Moreover, two tutorials were still missing from our collection started in Part 1.

First, there is the TPTP World by Geoff Sutcliffe from University of Miami. TPTP is a well known and established infrastructure that supports research, development, and deployment of Automated Theorem Proving (ATP) systems for classical logics.

Second, a tutorial was given by Harold Boley, University of New Brunswick, about PSOA RuleML. This integrated Positional-Slotted, Object-Applicative language permits a relation application to have an object identifier -- typed by the relation -- and, orthogonally, its arguments to be positional or slotted.

Last but not least, we are happy to share some impressions from RuleML 2015 with the community (click on the images to get an enlarged version):


We hope you enjoyed the conference and want to invite you to join us at the 10th International Web Rule Symposium from July 5 – July 8, 2016 at Stony Brook University, New York.

When Processes Rule Events

October 8, 2015 11:09 AM
Event creation is guided by processes: bus GPS info follow the bus scheduled route; RTLS information about the whereabouts of patients and nurses in a hospital is guided by the predefined schedule of work. As such, we thoroughly seek a method for mining, not the data, but rather the rules that guide data creation.
Keynote at, Avigdor Gal is a faculty member at the Faculty of Industrial Engineering & Management at the Technion. He received his D.Sc. degree from the Technion - Israel Institute ofTechnology in 1995 in the area of temporal active databases. During his studies, Avigdor has received the Miriam and Aaron Gutwirth Scholarship three years in a row (1993-1995). He has published more than 50 papers in journals (e.g. Journal of the ACM (JACM), ACM Transactions on Database Systems (TODS), IEEE Transactions on Knowledge and Data Engineering (TKDE), and the VLDB Journal), books (Temporal Databases: Research and Practice) and conferences on the topics of data integration, temporal databases, information systems architectures, and active databases.