Thomas Troels Hildebrandt

Thomas Troels Hildebrandt
IT University of Copenhagen · Theoretical Computer Science Section

PhD in Computer Science

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130
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Publications

Publications (130)
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Honorable mention award received at CSCW 2021 https://cscw.acm.org/2021/awards/
Article
Full-text available
Process design artifacts have been increasingly used to guide the modeling of business processes. To support users in designing and understanding process models, different process artifacts have been combined in several ways leading to the emergence of the so-called “hybrid process artifacts”. While many hybrid artifacts have been proposed in the l...
Chapter
This paper addresses the open technical problems of evolving executable, event-based process models by refinement, that is, by iteratively expanding a model until it has the required level of detail. Such iterative development is helpful because of the expectation that the next-step model is semantically compatible with the previous one, only with...
Chapter
Business processes, data, and run-time control state are all key elements in the design of enterprise applications. However, the different layers for processes, data, and control are usually represented using different technologies that must be explicitly combined and kept in sync. We introduce ReGraDa, a process definition and programming language...
Conference Paper
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This paper draws attention to new complexities of deploying artificial intelligence (AI) to sensitive contexts, such as welfare allocation. AI is increasingly used in public administration with the promise of improving decision-making through predictive modelling. To accurately predict, it needs all the agreed criteria used as part of decisions, fo...
Chapter
In this paper, we take technical and practical steps towards the modularisation of compliant-by-design executable declarative process models. First, we demonstrate by example how the specific language of timed DCR graphs is capable of modelling complex legislation, with examples from laws regulating the functioning of local governments in Denmark....
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This paper examines the nature of discretion in social work in order to debunk myths dominating prevalent debates on digitisation and automation in the public sector. Social workers have traditionally used their discretion widely and with great autonomy, but discretion has increasingly come under pressure for its apparent subjectivity and randomnes...
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Legal compliance is an important part of certifying the correct behaviour of a business process. To be compliant, organizations might hard-wire regulations into processes, limiting the discretion that workers have when choosing what activities should be executed in a case. Worse, hard-wired compliant processes are difficult to change when laws chan...
Chapter
Hybrid modeling approaches have been proposed to represent processes that have both strictly regulated parts and loosely regulated parts. Such process is so-called Knowledge-intensive Process (KiP), which is a sequence of activities based on intense knowledge use and acquisition. Due to these very particular characteristics, the first author previo...
Chapter
We provide the first formal model for declarative choreographies, which is able to express general omega-regular liveness properties. We use the Dynamic Condition Response (DCR) graphs notation for both choreographies and end-points. We define end-point projection as a restriction of DCR graphs and derive the condition for end-point projectability...
Chapter
The EcoKnow project strives to promote flexible case management systems in the public administration and empower end-users (i.e., case workers) to make sense of digitized models of the law. For this, a hybrid representation combining the declarative DCR notation with textual annotations depicting the law text and a simulation tool to simulate the e...
Chapter
The European General Data Protection Regulation (GDPR) gives primacy to purpose: Data may be collected and stored only when (i) end-users have consented, often explicitly, to the purposes for which that data is collected, and (ii) the collected data is actually necessary for achieving these purposes. This development in data protection regulations...
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We explore the complexity of reachability and run-time refinement under safety and liveness constraints in event-based process models. Our study is framed in the DCR\(^\star \) process language, which supports modular specification through a compositional operational semantics. DCR\(^\star \) encompasses the “Dynamic Condition Response (DCR) graphs...
Chapter
Situation faced: Exformatics, a Danish adaptive case-management vendor, wanted to leverage declarative process tools to support the flexible processes found at BRFkredit. However, switching from the more common flow-based notations to a declarative notation brought new challenges in terms of understandability. We undertook the project described in...
Conference Paper
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Based on ethnographic fieldwork, and the modelling of work processes at a medical department, this paper considers some of the opportunities and challenges involved in working with models in a complex work setting. The paper introduces a flexible modelling tool to CSCW, called the DCR Portal, and considers how it may be used to model complex work s...
Conference Paper
We investigate process mining for the declarative Dynamic Condition Response (DCR) graphs process modelling language. We contribute (a) a process mining algorithm for DCR graphs, (b) a proposal for a set of metrics quantifying output model quality, and (c) a preliminary example-based comparison with the Declare Maps Miner. The algorithm takes a con...
Conference Paper
We give the first non-interleaving early operational semantics for the pi-calculus which generalizes the standard interleaving semantics and unfolds to the stable model of prime event structures. Our starting point is the non-interleaving semantics given for CCS by Mukund and Nielsen, where the so-called structural (prefixing or subject) causality...
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We report on experiences from a case study applying a constraint-based process-modelling and -simulation tool, dcrgraphs.net, to the modelling and rehearsal of railway emergency response plans with domain experts. The case study confirmed the approach as a viable means for domain experts to analyse and rehearse emergency response plans, through the...
Conference Paper
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Case Management (CM) is a BPM technology for supporting flexible services orchestration. CM approaches like CMMN, an OMG standard, and GSM, one of CMMN’s core influences, use Event-Condition-Action rules, which can be inconsistent due to cyclic inter-dependencies between the rules; repairing such an inconsistent case management schema is difficult....
Conference Paper
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Modern form-based end-user interfaces are highly variable and need to adapt to the choices made by the user. To describe such adaptations programmatically is time and resource intensive and therefore more generic approaches are preferable. Form-based UIs are often very flexible: one usually has a large degree of freedom in the order in which fields...
Conference Paper
Software systems are increasingly used to support business processes and knowledge workflows within critical areas, including transportation, finance, healthcare and government. The support for such processes, which are at the same time unpredictable and subject to changing legal constraints, calls for flexibility, adaptability and compliancy. In t...
Article
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Psi-calculi constitute a parametric framework for nominal process calculi, where constraint based process calculi and process calculi for mobility can be defined as instances. We apply here the framework of psi-calculi to provide a foundation for the exploration of declarative event-based process calculi with support for run-time refinement. We fir...
Book
This volume contains the refereed joint proceedings of two initiatives that have been devoted to the formal foundations of complex systems: the workshops WS-FM:FASOCC 2014 and WS-FM/BEAT 2015. The 11th International Workshop on Web Services and Formal Methods: Formal Aspects of Services-Oriented and Cloud Computing, WS-FM 2014, took place in Eindh...
Conference Paper
Declarative or constraint-based business process and workflow notations, in particular DECLARE and Dynamic Condition Response (DCR) graphs, have received increasing interest in the last decade as possible means of addressing the challenge of supporting at the same time flexibility in execution, adaptability and compliance. However, the definition o...
Conference Paper
We study modularity, run-time adaptation and refinement under safety and liveness constraints in event-based process models with dynamic sub-process instantiation. The study is part of a larger programme to provide semantically well-founded technologies for modelling, implementation and verification of flexible, run-time adaptable processaware info...
Article
Full-text available
Psi-calculi are a parametric framework for nominal calculi, where standard calculi are found as instances, like the pi-calculus, or the cryptographic spi-calculus and applied-pi. Psi-calculi have an interleaving operational semantics, with a strong foundation on the theory of nominal sets and process algebras. Much of the expressive power of psi-ca...
Conference Paper
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We present a new declarative model with composition and hierarchical definition of processes, featuring (a) incremental refinement, (b) adaptation of processes, and (c) dynamic creation of sub-processes. The approach is motivated and exemplified by a recent case manage-ment solution delivered by our industry partner Exformatics A/S. The approach is...
Conference Paper
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We report on a recent industrial project carried out by Exformatics A/S in which the company used the declarative DCR Graphs notation to model and implement the grant application process of a Danish foundation. We present the process and discuss the advantages of the approach and challenges faced both while modelling and implementing the process. F...
Conference Paper
We show how a subpart of OWL ontologies and Semantic Web Rule Language (SWRL) rules can be represented as bigraphs and bigraphical reaction rules. While OWL allows for defining a static ontology and SWRL allows for inferring and adding more information to an ontology, we show that the bigraphical representation of ontologies and rules naturally all...
Conference Paper
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We present the first session typing system guaranteeing re-sponse liveness properties for possibly non-terminating communicating processes. The types augment the branch and select types of the standard binary session types for the π-calculus with a set of required responses, indicating that whenever a particular label is selected, a set of other la...
Conference Paper
A mobile cloud is a cloud infrastructure connecting to mobile devices with a variety of applications (apps). This paper proposes utilizing bigraphical reaction systems (BRSs) to model and analyze a mobile cloud including its contexts such as mobile location, power consumption, network bandwidth, and latency. Simulations and evaluations are performe...
Conference Paper
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Choreographies allow designers to specify the protocols followed by participants of a distributed interaction. In this context, adaptation may be necessary to respond to external requests or to better suit a changing environment (a self-update). Adapting the behavior of a participant requires to update in a coordinated way possibly all the particip...
Conference Paper
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We describe how the declarative Dynamic Condition Response (DCR) Graphs process model can be used for trustworthy adaptive case management by leveraging the flexible execution, dynamic composition and adaptation supported by DCR Graphs. The dynamically composed and adapted graphs are verified for deadlock freedom and liveness in the SPIN model chec...
Conference Paper
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Declarative workflow languages have been a growing research subject over the past ten years, but applications of the declarative approach in industry are still uncommon. Over the past two years Exformatics A/S, a Danish provider of Electronic Case Management systems, has been cooperating with researchers at IT University of Copenhagen (ITU) to crea...
Conference Paper
The efficient use of health care ressources requires the use of Information and Communication Technology (ICT). During a treatment process, patients have often been tested and partially treated with different diagnoses in mind before the precise diagnosis is identified. To use ressources well it becomes necessary to adapt the prescribed treatments...
Article
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We conservatively extend the declarative Dynamic Condition Response (DCR) Graph process model, introduced in the PhD thesis of the second author, to allow for discrete time deadlines. We prove that safety and liveness properties can be verified by mapping finite timed DCR Graphs to finite state transition systems. We exemplify how deadlines can int...
Article
We present the BigMC tool for bigraphical reactive systems that may be instantiated as a verification tool for any formalism or domain-specific modelling language encoded as a bigraphical reactive system. We introduce the syntax and use of BigMC, and exemplify its use with two small examples: a textbook “philosophers” example, and an example motiva...
Conference Paper
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We propose the recently introduced declarative and event-based Dynamic Condition Response (DCR) Graphs process model as a formal basis for modular implementation of context-sensitive and aspect-oriented processes. The proposal is supported by a new join operator allowing modular composition and refinement of DCR Graphs. We give small illustrative e...
Conference Paper
This paper proposes a new theory of multiparty session types extended with propositional assertions and symmetric sum types for modelling collaborative distributed workflows. Multiparty session types statically guarantee that workflows are type-safe and deadlock-free, facilitate automatic generation of participant-specific (“local”) workflow protoc...
Article
We present Big Red, a visual editor for bigraphs and bigraphical reactive systems, based upon Eclipse. The editor integrates with several existing bigraph tools to permit simulation and reachability analysis of bigraphical models. We give a brief introduction to the bigraphs formalism, and show how these concepts manifest within the tool using a sm...
Article
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Motivated by the response pattern for property specifications and applications within flexible workflow management systems, we report upon an initial study of modal and mixed transition systems in which the must transitions are interpreted as must eventually, and in which implementations can contain may behaviors that are resolved at run-time. We p...
Article
We present the first version of PEPL, a declarative Process-oriented Event-based Programming Language based on the recently introduced Dynamic Condition Response (DCR) Graphs model. DCR Graphs allow for specification, distributed execution and verification of pervasive, event-based workflow and business processes by declaring condition, response, e...
Article
Bigraphical Reactive Systems have been proposed,as a meta model,for global ubiquitous computing,generalising process calculi for mobility such as the pi-calculus and the Mobile Ambients calculus as well as graphical models,for con- currency such as Petri Nets. We investigate in this paper how,Bigraphical Reactive Systems represented as Reactive XML...
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Monoidal categories of acyclic graphs capture the no-tion of multi-hole context, pervasive in syntax and seman-tics. Milner's bigraphs is a recent example. We give a method for generalising such categories to monoidal closed categories of acyclic graphs. The method combines the Int-construction, lifting traced monoidal categories to com-pact closed...
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We present a model checking tool for Bigraphical Reactive Systems that may be instantiated as a model checker for any formalism or domain-specific modelling language encoded as a Bigraphical Reactive System. We describe the implementation of the tool, and how it can be used to verify correctness properties of some infinite-state models by applying...
Conference Paper
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We give a general technique for safe distribution of a declarative (global) process as a network of (local) synchronously communicating declarative processes. Both the global and local processes are given as Dynamic Condition Response (DCR) Graphs. DCR Graphs is a recently introduced declarative process model generalizing labelled prime event struc...
Article
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We explore logical reasoning for the global calculus, a coordination model based on the notion of choreography, with the aim to provide a methodology for specification and verification of structured communications. Starting with an extension of Hennessy-Milner logic, we present the global logic (GL), a modal logic describing possible interactions a...
Article
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We present Dynamic Condition Response Graphs (DCR Graphs) as a declarative, event-based process model inspired by the workflow language employed by our industrial partner and conservatively generalizing prime event structures. A dynamic condition response graph is a directed graph with nodes representing the events that can happen and arrows repres...
Conference Paper
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We present a formal technique for safe distribution of workflow processes described declaratively as nested Dynamic Condition Response (DCR) Graphs and apply the technique to a distributed healthcare workflow. Concretely, we provide a method to synthesize from a nested DCR Graph and any distribution of its atomic events a set of local process graph...
Conference Paper
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We present a case study of the use of Dynamic Con- dition Response (DCR) Graphs, a recently introduced declarative business process model, in the design of a cross-organizational case management system being developed by Exformatics A/S, a Danish provider of knowledge and workflow management systems. We show how DCR Graphs allow to capture directly...
Article
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We propose a mechanism for the vertical refinement of bigraphical reactive systems, based upon a mechanism for limiting observations and utilising the underlying categorical structure of bigraphs. We present a motivating example to demonstrate that the proposed notion of refinement is sensible with respect to the theory of bigraphical reactive syst...
Conference Paper
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We present an extension of the recently introduced declarative process model Dynamic Condition Response Graphs (DCR Graphs) to allow nested sub-graphs and a new milestone relation between events. The extension was devel-oped during a case study carried out jointly with our industrial partner Exformat-ics, a danish provider of case and workflow mana...
Article
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We present a case study of a design of a distributed case management system using Dynamic Condition Re-sponse (DCR) Graphs, a recently proposed declarative notation for distributed processes. The case study was carried out jointly with our industrial partner Exformatics, a danish provider of knowledge and workflow man-agement systems. We present an...
Conference Paper
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We present the first direct formalization of the semantics of inclusive gateways as described in the Business Process Modeling Notation (BPMN) 2.0 Beta 1 specification. The formal semantics is given for a minimal subset of BPMN 2.0 containing just the inclusive and exclusive gateways and the start and stop events. By focusing on this subset we achi...
Article
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Recently we have presented distributed dynamic condition response structures (DCR structures) as a declarative process model conservatively generalizing labelled event structures to allow for finite specifications of repeated, possibly infinite behavior. The key ideas are to split the causality relation of event structures in two dual relations: th...
Article
Milner Robin . The space and motion of communicating agents. Cambridge University Press, 2009, 212 pp. - Volume 16 Issue 2 - Thomas Hildebrandt
Article
This issue of Mathematical Structures in Computer Science contains three papers selected from the 15th International Workshop on Expressiveness in Concurrency (EXPRESS'08) held on 23 August 2008 in Toronto (Canada) as a satellite event of CONCUR'08.
Conference Paper
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We present a systematic study of the WS-BPEL 2.0 standard based on two complementary methods: the process of constructing a new high-level WS-BPEL implementation driven by the structure of the standard, and an empirical evaluation of existing interpretations of the standard reflected in five widely available WS-BPEL-implementations, both commercial...
Conference Paper
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The fundamental primitives of Concurrent Constraint Programming (CCP), \({\mathit{tell}}\) and \({\mathit {ask}}\), respectively adds knowledge to and infers knowledge from a shared constraint store. These features, and the elegant use of the constraint system to represent the abilities of attackers, make concurrent constraint programming and timed...
Conference Paper
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We propose a novel and uniform approach to type systems for (process) calculi, which roughly pushes the challenge of designing type systems and proving properties about them to the meta-model of bigraphs. Concretely, we propose to define type systems for the term language for bigraphs, which is based on a fixed set of elementary bigraphs and operat...
Conference Paper
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We present a field study of oncology workflow, involving doctors, nurses and pharmacists at