Colored Petri Net

After a survey of some approaches for modeling hybrid systems by means of Petri nets (t-time Petri nets, colored Petri nets, hybrid Petri nets and differential predicate transition nets), this paper illustrates how these formal models can be used for simulation and validation. It is shown how it was possible to use aggregated qualitative models concurrently with detailed ones.

Software testing is one of the most widely used methods for quality assurance and fault detection purposes. However, it is one of the most expensive, tedious and time consuming activities in software development life cycle. Code-based and specification-based testing has been going on for almost four decades. Model-based testing (MBT) is a relatively new approach to software testing where the

Abstract. E-contracting, ie, establishing and enacting electronic contracts, has become important because of technological advances (eg, the availability of web services) and more open markets. However, the establishment of an e-contract is complicated and error prone. There are multiple negotiation styles ranging from auctions to bilateral bargaining. This paper provides an approach for modeling multi-party negotiation protocols in colored Petri nets. It is shown how different negotiation styles can be modeled in a unified and ...

This manuscript addresses the creation of scenario-based models to reason about the behavior of existing industrial information systems. In our approach the system behavior is modeled in two steps that gradually introduce detail and formality. This manuscript addresses the first step, where text-based descriptions, in the form of structured rules, are used to specify how the system is or should be regulated. Those rules can be used to create behavioral snapshots, which are collections of scenario-based descriptions that represent different instances of the system behavior. Snapshots are specified in an intuitive and graphical notation that considers the elements from the problem domain and permit designers to discuss and validate the externally observable behavior, together with the domain experts. In the second step (not fully covered in this manuscript), the system behavior is formalized with an executable model. This formal model, which in our approach is specified using the Colored Petri Net (CP-nets) language, allows the system internal behavior to be animated, simulated, and optimized. The insights gained by experimenting with the formal model can be subsequently used for reengineering the existing system.

A key ingredient in system and organization modeling is modeling business processes that involve the collaborative participation of different teams within and outside the organization. Recently, the use of the Unified Modeling Language (UML) for collaborative business modeling has been increasing, thanks to its human-friendly visual representation of a rich set of structural and behavioral views, albeit its unclear semantics. In the meantime, the use of the Web Ontology Language (OWL) has also been emerging, thanks to its clearly-defined semantics, hence being amenable to automatic analysis and reasoning, although it is less human friendly than, and also perhaps not as rich as, the UML notationespecially concerning processes, or activities. In this paper, we view the UML and the OWL as being complementary to each other, and exploit their relative strengths. We provide a mapping between the two, through a set of mapping rules, which allow for the capture of UML activity diagrams in an OWL-ontology. This mapping, which results in a formalization of collaborative processes, also sets a basis for subsequent construction of executable models using the Colored Petri Nets (CPN) formalism. For this purpose, we also provide appropriate mappings from OWL-based ontological elements into CPN elements. A case study of a mortgage granting system is described, along with the potential benefits and limitations of our proposal. 727 The modeling of collaboration processes encompasses the conceptual modeling of a particular domain along with simulation of executable business process models involved in that domain . A key factor in this process is that, besides the models themselves, their inherent semantics should also be shared in order to achieve a common understanding between the collaborating participants . AMENITIES [25] is a methodological framework for the study and development of collaborative systems which extends and makes use of the Unified Modeling Language (UML) . In this framework, different models are subsequently used by stakeholders (e.g., system architects, system analysts, users, testers, programmers, etc.) in order to model and analyze the main characteristics of these kinds of systems (e.g. system structure and behavior to be supported). These models range from those which provide a structural view of a collaborative system (e.g., class and object diagrams) to those which offer a behavioral view (e.g., activity diagrams and state machines).

This report examines and classifies the characteristics of signatures used in misuse intrusion detection. EfficienL algorithms to matcll paHerns in some of these classes are described. A generalized model for matclling intrusion signatures based on Colored Petri Nets is presented, and some of its properties arc derived.

In management theory of the last decades, much importance has been attached to a process-oriented perspective on organizational (re)structuring. Yet to date, organizations still experience difficulties in applying this process-oriented perspective to the design and maintenance information systems.

Purpose – XML has spread beyond the computer science fields and reached other areas such as, e-commerce, identification, information storage, instant messaging and others. Data communicated over these domains are now mainly based on XML. Thus, allowing non-expert programmers to manipulate and control their XML data is essential. The purpose of this paper is to present an XA2C framework intended

Collaborative business process can become unreliable when business partners collaborate in a peerbased fashion without central control. Therefore, reliability checking becomes an important issue that needs to be dealt with for any generic solution in managing business collaboration. In this paper, we propose a novel Choreographical Business Transaction Net (CoBTx-Net) to model collaborative business process and to manage the collaboration by individual participants. Furthermore three reliability properties named Time-embedded dead marking freeness, Interorganizational dead marking freeness, and Collaborative soundness are defined based on CoBTx-Net to verify (1) the violation of time constraint, (2) collaborative logic conflicts, and (3) the improper termination from individual organizations.

A model-based agent system model for medicine usage management is presented and formally analysed. The model incorporates an intelligent ambient agent model that has an explicit representation of a dynamical system model to estimate the medicine level in the patient's body by simulation, is able to analyse whether the patient intends to take the medicine too early or too late, and can take measures to prevent this.

& Conclusions-This paper presents a methodology and an example of risk assessment of functional-requirement specifications for complex real-time software systems. A heuristic risk-assessment technique based on CPN (colored Petri-net) models is presented. This technique is used to classify software functional-requirement specification components according to their relative importance in terms of such factors as severity and complexity. A dynamic complexity measure, based on concurrence in the functional requirements, is introduced. This technique is applied on the Earth Operation Commanding Center (EOC COMMANDING), a large component of the NASA Earth Observing System (EOS) project. Two specification models of the system are considered. Results of applying this technique to both models are presented.

Computer system reliability is conventionally modeled and analyzed using techniques such as fault tree analysis (FTA) and reliability block diagrams (RBD), which provide static representations of system reliability properties. A recent extension to RBD, called dynamic reliability block diagrams (DRBD), defines a framework for modeling dynamic reliability behavior of computer-based systems. However, analyzing a DRBD model in order to locate and identify design errors, such as a deadlock error or faulty state, is not trivial when done manually. A feasible approach to verifying it is to develop its formal model, and then analyze it using programmatic methods. In this paper, we first define a reliability markup language (RML) that can be used to formally describe DRBD models. Then we present an algorithm that automatically converts a DRBD model into a colored Petri net (CPN). We use a case study to illustrate the effectiveness of our approach and demonstrate how system properties of a DRBD model can be verified using an existing Petri net tool. Our formal modeling approach is compositional, thus it provides a potential solution to automated verification of DRBD models.

Considers a modern warehousing system composed of a number of aisles, each one served by a crane and sided by a pair of racks, and a shuttle which moves along a 1D path placed orthogonally with respect to the aisles' axis. The main operations performed by the control system concern the optimization of the cranes and shuttle movements. Regarding the cranes, we propose an algorithm for optimizing the sequencing of dual command (storage and retrieval) cycles, so to maximize the throughput. As for the shuttle, an algorithm is proposed to optimize the scheduling of the shuttle operations; the performance of the algorithm is evaluated and compared with the case in which no optimization is considered. A further contribution of the paper is the derivation of the model of a real warehousing system, by means of a colored Petri net approach. Such a model is then used to show and validate the effectiveness of the proposed algorithms

In a multistage interconnection network (MIN) the calculation of the number of permutations of the input terminals into the output terminals is a classic difficult problem. In this paper, we introduce an innovative technique based on Colored Petri Nets (known as CP-nets or CPNs) that will allow us to analyze the permutation capability of arbitrary MINs. We show how to verify whether a MIN is rearrangeable through the state space analysis of the associated CP-net and we measure the permutation capability of non-rearrangeable MINs in terms of the permutations that can be generated. The proposed approach takes advantage of powerful existing software tools, particularly, CPNTools, which is used to explore the occurrence graphs of CP-nets and determine the set of permutations performed by the modeled MINs. This new technique is easy to use and can be efficiently applied to MINs made of cross-bar switches.

Service-Oriented Architecture (SOA) is achieving widespread acceptance in a variety of enterprise systems, due to its inherent flexibility and interoperability, improving upon the more tradition and less supportable “stovepipe” approach. The high degree of concurrency and both synchronous and asynchronous communications inherent in SOA makes it a good candidate for a Petri Nets based model driven development (MDD). Such an approach, with its underlying verification and validation implications, becomes more crucial in mission-critical applications, such as those with defense implications. This paper reports on our experience with using Colored Petri Nets (CPNs) for model driven development and quality assessment of a defense-targeted serviceoriented software architecture. We identify features of CPN that have resulted in ease of adoption as a modeling tool in our present setting. Preliminary results are provided which support the use of CPNs as a basis for model driven software devel...

Service-Oriented Architecture (SOA) is achieving widespread acceptance in a variety of enterprise systems, due to its inherent flexibility and interoperability, improving upon the more tradition and less supportable "stovepipe" approach. The high degree of concurrency and both synchronous and asynchronous communications inherent in SOA makes it a good candidate for a Petri Nets based model driven development (MDD). Such an approach, with its underlying verification and validation implications, becomes more crucial in mission-critical applications, such as those with defense implications. This paper reports on our experience with using Colored Petri Nets (CPNs) for model driven development and quality assessment of a defense-targeted serviceoriented software architecture. We identify features of CPN that have resulted in ease of adoption as a modeling tool in our present setting. Preliminary results are provided which support the use of CPNs as a basis for model driven software development, and verification and validation (V&V) for quality assurance of highly concurrent and mission-critical SOAs.

Petri Nets provide a graphical notation for modeling systems and performing analysis. Colored Petri Nets (CPNs) combine the strengths of ordinary Petri Nets with a high level programming language, making them more suitable for modeling large systems. A CPN model is an executable representation of a system that can be analyzed through simulation. CPN models are built using CPN Tools, a graphical software tool and interface used to create, edit, simulate, and analyze models. This tutorial is meant to introduce the reader to the vocabulary and constructs of CPNs and illustrate the use of CPN Tools in creating and simulating models by means of a familiar, simple example. In particular, we show how to create a CPN model of the call center example presented by White and Ingalls in their tutorial Introduction to Simulation.

Understanding the operations of a large "net-centric system-of-systems" requires in-depth knowledge of the interfaces and the interactions among the various systems, subsystems, and components. Architectural modeling can help in reducing the complexity involved in designing large networked systems. This paper demonstrates a modeling approach for network centric systems. An example of such a complex system is the Global Earth Observation System of Systems (GEOSS)-a system for monitoring and collecting information related to Earth's resources. The GEOSS is an evolving complex network centric system. The modeling of the GEOSS has been demonstrated using the Systems Modeling Language (SysML). In this paper, 203 architecture representation using SysML demonstrates an object-oriented approach of model development. This paper discusses issues related to architecture description, development, presentation, and integration for the chosen domain. This paper also highlights some of the differences between SysML, which is used to model a wide range of systems, and Unified Modeling Language (UML), which is primarily used to model information systems only. Finally, in order to synthesize an executable model from the static views developed using SysML, Colored Petri-nets (CP-nets) have been used. The executable model, constructed using CP nets, is used to validate the architecture against the static model. Overall, this research defines a methodology to model and simulate complex network centric system of systems in order to understand and simulate their behavior using a scenario based approach.

This paper presents an ARENA®-based library for the development of Timed Colored Petri Net (TCPN) models. In this way, the strengths of Petri Nets and Discrete Event Simulation (DES) are combined in a powerful tool for modeling and analysis of systems. The use of the library is illustrated on a cosmetics manufacturing facility in Bogotá (Colombia). This facility was modeled via both TCPNs and a classical DES methodology. Extensive analysis shows the advantages and disadvantages of each approach.

In this paper, we propose a formal description for the dynamic verification of an Object-Rule Hybrid Knowledge-based System (HKBS), capitalizing on the work carried out within the verification framework of Frame-Rule Hybrid Expert Systems. The main idea is to model an HKBS by means of a Colored Petri Network (CPN). In this way, method invocations, state class changes, rules and productions will be modeled as components of the CPN. Detection and analysis of the HKBS will be carried out by the construction and analysis of the markings graph, which results from the inference process.

In the past we have shown that it is possible to take an architecture description that conforms to DODAF and convert it to an executable model to support rigorous evaluation. We now have a proof of concept that demonstrates the feasibility of making the conversion to the executable model automatically. Implementing this automatic translation will enable architects to apply more rigorous analysis and evaluation approaches to complex architecture evaluation problems such as determining the agility in particular architecture designs that are based on information sharing. This paper describes the issues in automatic translation of architectures that are based on either the Structured Analysis or the Object Oriented approaches into the rigorous executable modeling language of Colored Petri Nets. The paper includes a proof of concept case study and briefly discusses the advantages of using the executable model in evaluating logical, behavioral, and performance aspects of the architecture.

Traditionally, the semiconductor manufacturing industry has been driven by continuous technological advancement of the underlying production processes. Yet, as the industry matures, mere technology development is no longer suf®cient. The effective deployment and exploitation of the system production capacity and operational capability become critical for competitive success. Hence, currently, there is an increasing interest towards the development of a control paradigm/ framework that will allow the effective and ef®cient deployment and operation of contemporary fabs, including the upcoming 300 mm fab. The research program presented in this paper seeks to de®ne a detailed modeling and control framework for the real-time 300 mm fab operations, by exploiting and integrating emerging results in Discrete Event Systems theory. The proposed approach is demonstrated through a small-scale example, modeling the operation of a 300 mm fab bay. Furthermore, in addition to the development of the formal speci®cation, the presented program will also implement the proposed fab modeling and control framework in a Web-based simulation platform, that will function as a fab (re-)con®guration and control synthesis tool for the fab control engineer, and as an educational tool for manufacturing system modeling and control. #

Purpose – XML has spread beyond the computer science fields and reached other areas such as, e-commerce, identification, information storage, instant messaging and others. Data communicated over these domains are now mainly based on XML. Thus, allowing non-expert programmers to manipulate and control their XML data is essential. The purpose of this paper is to present an XA2C framework intended

Accurate identification of misuse is a key factor in determining appropriate ways to protect systems. Modern intrusion detection systems often use alerts from different sources such as hosts and sub-networks to determine whether and how to respond to an attack. However, alerts from different locations should not be treated equally. We propose improving and assessing alert accuracy by incorporating an algorithm based on the exponentially weighted Dempster-Shafer (D-S) Theory of Evidence. Our approach uses D-S theory to combine beliefs in certain hypotheses under conditions of uncertainty and ignorance, and allows quantitative measurement of the belief and plausibility in our detection results. Our initial evaluations on the DARPA IDS evaluation data set show that our alert fusion algorithm can improve alert quality over those from Hidden Colored Petri-Net (HCPN) based alert correlation components installed at the demilitarized zone (DMZ) and inside network sites. Due to alert confidence fusion in our example, the detection rate rises from 75% to 93.8%, without adversely affecting the false positive rate.

This paper presents an ARENA®-based library for the development of Timed Colored Petri Net (TCPN) models. In this way, the strengths of Petri Nets and Discrete Event Simulation (DES) are combined in a powerful tool for modeling and analysis of systems. The use of the library is illustrated on a cosmetics manufacturing facility in Bogotá (Colombia). This facility was modeled via both TCPNs and a classical DES methodology. Extensive analysis shows the advantages and disadvantages of each approach.

This report examines and classifies the characteristics of signatures used in misuse intrusion detection. EfficienL algorithms to matcll paHerns in some of these classes are described. A generalized model for matclling intrusion signatures based on Colored Petri Nets is presented, and some of its properties arc derived.

The integration of Software Fault Tree (SFT), which describes intrusions and Coloured Petri Nets (CPNs) that specifies design, is examined for an Intrusion Detection System (IDS). The IDS under development is a collection of mobile agents that detect, classify, and correlate the system and network activities. SFTs, augmented with nodes that describe trust, temporal and contextual relationships, are used to describe intrusions. CPNs for intrusion detection are built using CPN templates created from the augmented SFTs. Hierarchical CPNs are created to detect critical stages of intrusions. The agentbased implementation of the IDS is then constructed from the CPNs. Examples of intrusions and descriptions of the prototype implementation are used to demonstrate how the CPN approach has been used in the development of the IDS.

In distributed environments, the shared resources access control by mutual exclusion paradigm is a recurrent key problem. To cope with the new constraints implied by recently developed large scale distributed systems like grids, mutual exclusion algorithms become more and more complex and thus much harder to prove and/or verify. In this article, we propose the formal modeling and the verification of a new generic hierarchical approach. This approach is based on the composition of classical already proof checked distributed algorithms. It overcomes some limitations of these classical algorithms by taking into account the network topology latencies and have a high scalability where centralized ones don't. We also have formalized the properties of the mutual exclusion paradigm in order to verify them against our solution. We prove that our compositional approach preserves theses properties under the assumption that all used plain algorithms assert them. This verification by formal method checkers was eased by the efficient use of already proved mutual exclusion algorithms and the reduction of state spaces by exploiting the symmetries.

We give a high-level overview of our recent results which extend and unify the lines of research initiated by Meseguer and Montanari under the motto "Petri nets are monoids", and by Marti-Oliet, Meseguer and other authors in their linear logic axiomization of Petri nets. In particular, we investigate the use of rewriting logic, which was partially inspired by the two aforementioned approaches, as a unifying semantic framework for different Petri net models. To this end, we equip place/transition nets with a rewriting semantics which is sound and complete in the strong categorical sense of a natural isomorphism between the Best-Devillers process semantics and the semantics obtained via rewriting logic. In addition to place/transition nets we consider algebraic net specifications which subsume colored Petri nets and we show how a corresponding sound and complete rewriting semantics can be established at this level. Furthermore, we discuss how rewriting logic can be used to represent other important extensions of the basic Petri net model such as place/transition nets with test arcs and timed Petri nets. Apart from the conceptual unification of different models in a field which has to cope with increasing diversity, this work has interesting practical applications ranging from the execution and analysis of Petri net models, using a rewriting engine such as Maude, to formal verification taking advantage of the logical side rather than the operational side of rewriting logic.

One of the challenging problems for software developers is guaranteeing that a system as built is consistent with its architectural design. In this paper, we describe a technique that uses runtime observations about an executing system to construct an architectural view of the system. In this technique, we develop mappings that exploit regularities in system implementation and architectural style. These mappings describe how low-level system events can be interpreted as more abstract architectural operations and are formally defined using Colored Petri Nets. In this paper, we describe a system, called DiscoTect, that uses these mappings and we introduce the DiscoSTEP mapping language and its formal definition. Two case studies showing the application of DiscoTect suggest that the tool is practical to apply to legacy systems and can dynamically verify conformance to a preexisting architectural specification.

One of the key issue in designing a variable structure organization is to find the constraints on folding the appropriate fixed structures for different situations into one variable structure. The Coordination Constraint must be satisfied to ensure the folding is valid s o that the variable structure organization is a feasible one. An algorithm for checking t h i s constraint is introduced.

Concurrent competition for finite resources by multiple parts in flexible manufacturing systems (FMS's) results in deadlock. This is an important issue to be addressed in the operation of the system. A Petri net model, called colored resource-oriented Petri net (CROPN), is developed in this paper. The concurrent resource contention and the important characteristics of the production processes necessary for deadlock control are well modeled by this model. Based on the developed model, necessary and sufficient conditions and an efficient control law are presented for deadlock-free operation in FMS's. This control law is a policy of dynamic resource allocation. It determines when a resource can be allocated to which job to avoid deadlock. This control law allows as many active parts as possible to be in the system, while deadlock is totally avoided. This control law is easy to implement and can be embedded into the real-time scheduler. A simple example is used to illustrate the application of the approach.

Database administrators need to compute closure of functional dependencies (FDs) for normalization of
database systems and enforcing integrity rules. Colored Petri net (CPN) is a powerful formal method for modelling and verification of various systems. In this paper, we modelled Armstrong's axioms for automatic proof generation of a new FD rule from initial FD rules using CPN. For this purpose, a CPN model of Armstrong's axioms presents and initial FDs considered in the model as initial color set. Then we search
required FD in the state space of the model via model checking. If it exists in the state space, then a recursive ML code extracts the proof of this FD rule using further searches in the state space of the model.

This paper describes the use of timed hierarchical colored Petri nets (timed CPN) in the development, simulation and analysis of flexible manufacturing systems models. The major aim is to propose a systematized hybrid methodology, using refinement and compositions to construct models that represent a real system and conserve some properties of interest. The highest abstraction level of the model is

Computer component fabrication is approaching physical limits of traditional photolithographic fabrication techniques. An alternative computer architecture may be enabled by the rapidly maturing field of nanotechnology, and consist of nanomechanical computational machines similar to those first proposed by Eric Drexler, or other nanoscale components. In this study, we propose the design of a nanocompiler which targets a simulated hydrocarbon assembler. The compiler framework and resulting nano-mechanical machine is simulated using a component-level Colored Petri Net model of a 32-bit adder and an atomic-level gate simulator. Future work is proposed to extend the framework to simulate a full range nano-mechanical processing components.

This study aims at presenting a hybrid Flexible Manufacturing System "HFMS" short-term scheduling problem. Based on the art state of general scheduling algorithms, we present the metaheuristic, we have decided to apply for a given example of HFMS. That was the study of Simulated Annealing Algorithm SA. The HFMS model based on hierarchical Petri nets, was used to represent static and dynamic behavior of the HFMS and design scheduling solutions. Hierarchical Petri nets model was regarded as being made up a set of single timed colored Petri nets models. Each single model represents one process which was composed of many operations and tasks. The complex scheduling problem was decomposed in simple sub-problems. Scheduling algorithm was applied on each sub model in order to resolve conflicts on shared production resources.

Nowadays, rules make part of any software system including real-time applications and games, meanwhile an event can trigger many different rules according to the conditions controlling these rules. Although rules are core part to many kinds of systems, its maintenance and update are not easy without affecting the whole application. Hence, many systems have presented rules as a separate layer from the application; such as: SAMOS, Sentinel, Snoop, SnoopIB and CCPN. CCPN is a model that was used in an Amplified CDBB-500 architecture; which is a system supporting active database within its architecture. In this paper, we propose some extensions on CCPN to be able to present rules as a separate layer from the application, to support time-based events, and to add other important features which were agreed and implemented in other systems such as: Snoop and SnoopIB.

In this paper we review several approaches for the performance evaluation of business workflows and propose an approach based on Generalized Stochastic Petri Nets, which presents desirable characteristics, such as analytic solutions. We present a case study demonstrating the application of our proposal and compare the results with that obtained by a colored Petri net model.

Service Oriented Architectures (SOAs) are rapidly becoming an accepted means for network information exchange across heterogeneous fabrics of nodes. In architecture, an SOA is a system of systems (SoS) with complex interactions. Owing to SOA benefits of flexibility, interoperability, loose coupling, and reusability, the Department of Defense (DoD) has a future SOA framework for defense applications known as Net-Centric Enterprise Solutions for Interoperability (NESI). This paper details the modeling effort of a Multi-Channel Service Oriented Architecture (MCSOA), an enhanced SOA for DoD's requirements. MCSOA's Discovery protocol enables location transparency, availability awareness, service guarantees, context-based routing, and fault-tolerance. To handle MCSOA's complexities we adopted hybrid modeling, using Colored Petri Nets for the internal structure and interactions, and Extend/MESA for data exchanges at the network level. Reliable Extend/MESA models need error-free internal interactions, which we validate in the underlying CPN model, The paper contains a brief description of our models and validation results.

Changes in objectives, in resources, or in the environment may necessitate the adaptation of an organization from one form to another. However, in many cases, the organizations need to continue functioning while adaptation takes place, i.e., it is not possible to stop the organizational activity in order to reorganize, and then start again. In this case, adaptation can be expressed as a morphing process in which the organization transitions from one form with its attendant task allocation to a different one through a series of incremental steps that preserve overall functionality and performance. Coordination between organization members during adaptation is critical. A computational model for this type of organizational adaptation at the operational level is presented. The model is implemented using the Colored Petri Net formulation of discrete event dynamical systems. A design methodology that utilizes this model is outlined and a simple example is used to illustrate the approach.

This paper deals with a formal method for the study of the backward reachability analysis applied on Colored Petri Nets (CPN). The proposed method proceeds in two steps : 1) it translates CPN to terms of the Multiplicative Intuitionistic Linear Logic (MILL); 2) it proves sequents by constructing proof trees. The translation from CPN to MILL must respect some properties such as the semantic associated to tokens. That is why, the First-Order MILL (MILL1) is used for translation. The reachability between two markings, the initial marking and the final marking, is expressed by a sequent which can be proven (if the initial marking is backward-reachable from the final one) using first-order terms unification and/or marking enhancement.

, the problem remains that video is generally considered too detailed and cumbersome to work with. Even those who strongly advocate gathering detailed observations of use seek ways to abstract their findings, e.g., Simon's (1993) Verbal Protocol Analysis and Holzblatt's (1998) Contextual Inquiry. How can we take advantage of this highly contextual, qualitative data to generate usable design abstractions without losing the key details?