sufficient to simply exchange data that is syntactically correct, it is also important to ensure that the information ... Lastly, file sharing with the system engineering.
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Levels of SysML Compatibility for Collaborative Human System Development Holly A. H. Handley, PhD, PE, Matthew Amissah & Cansu Kandemir Old Dominion University, Norfolk, VA Developing human centered systems across multiple design and development teams requires a common framework to ensure seamless transition of models between collaborators. It is not sufficient to simply exchange data that is syntactically correct, it is also important to ensure that the information exchanged has shared meaning among team members. A current design project that included human architecting, human performance modeling and system engineering teams provided the foundation for a level of compatibility framework for Model Based System Engineering (MBSE) using the System Modeling Language (SysML). This framework provides descriptions of four different levels of model maturity that can be used for collaborative development. At each stage, the benefits of the model are described as well as its limitations. The Levels of SysML Compatibility can be used to integrate the Human Views, Soldier System library models and IMPRINT simulations to produce a comprehensive human system modeling approach.
Copyright 2016 by Human Factors and Ergonomics Society. DOI 10.1177/1541931213601393
INTRODUCTION The need to define levels of compatibility for models produced using the System Modeling Language (SysML) became apparent while identifying the requirements for a Model Based System Engineering (MBSE) collaborative development. A research initiative, termed the Model Based Soldier Decision Framework (MBSDF) was created to improve collaboration between human system architecting processes, human performance modeling, and soldier level system engineering. MBSE is the application of modeling to support the system engineering process; it emphasizes the use of integrated models to communicate the outcomes of the engineering process vice the traditional document based outcomes (INCOSE, 2015). SysML is a graphical modeling language based on the Unified Modeling Language (UML) with extensions to support the system engineering community; it is often used as a general purpose visual modeling language for system engineering applications to create the models for MBSE (Friedenthal, et al., 2012). The objective of the MBSDF initiative was to apply SysML principles to identify the requirements of a model-based, multiperspective decision process tying human system integration and system engineering to a human architecture viewpoint. The MBSDF collaboration envisioned using the SysML models as a software repository of design information. However, the requirements for creating the models in a way that made them usable across the teams, as well as the requirements for sharing them among the teams, needed to be identified. The concept of "levels of compatibility" was developed to ensure that team
members could share models without issues at either the system or data level. The resulting Levels of SysML Compatibility supports three development teams participating in the MBSDF initiative. The Human View architecting process (Handley & Knapp, 2014) was used to provide a data repository of human system information. These views were captured as SysML diagrams focused on identifying the relationships between specific roles and responses to different tasks present in the system environment. This data was then made available to the Improved Performance Research Integration Tool (IMPRINT) human performance modeling team. This model requires a task network representation of user actions for operator workload and system performance analysis (Mitchell, 2009). The Human View SysML models can be converted to the IMPRINT formalism with some manipulations required by the modeler; one of the goals of the level of compatibility initiative is to minimize the number of interventions. Additionally, representation of soldier tasks and equipment exist as a library of SysML models from the Soldier System engineering group. The second goal of the levels of compatibility imitative is to identify requirements so that the architecting effort can seamlessly link to the preexisting soldier library resulting in a higher fidelity model. Increasing the focus on the integration of the Human View architecting process and the System Engineering model library, as well as facilitating the transition from the Human View to the IMPRINT simulation will help establish a model based system engineering process supporting trade-off analysis of soldier acquisition decisions.
Proceedings of the Human Factors and Ergonomics Society 2016 Annual Meeting
PRACTICE INNOVATION The initial challenge of the MBSDF design collaborations was to overcome the divergent terminology and modeling approaches among the human architecting, human performance simulation and system engineering teams. Initial results from files exchanged between the teams indicated the need to define compatibility requirements on multiple levels. First, differences in SysML program versions and email protocols signified the need for establishing technical requirements that included versioning, file size, etc. Secondly, initial file sharing with the human performance modeling team identified the need to define SysML constructs that resulted in minimum interventions for the IMPRINT tool; modelers arrange networks to ensure readability and conformance with SysML when a new human performance model is created. Lastly, file sharing with the system engineering team identified the need to create SysML constructs so that role and task data can correctly “reference” or link to existing engineering models. Linking to existing models would provide soldier, task, and weapon data at the level of detail required for the IMPRINT model without having to recreate it in the human architecture models. These initial interactions identified the need to specify technical, syntax and semantic information, and executable interoperability requirements between the three development teams. Thus, in order to ensure compatibility of SysML models, best practices need to be put into place to provide the ability to exchange data without inconsistencies in content or context. This implies that interoperability is required among the collaborative teams to ensure seamless sharing of information. Three general levels of interoperability can be described: technical, informational, and organizational (NIST, 2010). Technical interoperability defines the “hardware and software” to connect systems or teams. In a collaborative team setting, it can be achieved by ensuring that all team members can send and receive email and open attached files using an agreed upon software program. Informational interoperability focuses on ensuring that the data exchanged is comprehensible and useful for the other teams. In this case, it requires all teams to agree what the data represents in the SysML models, and to adhere to a set of mutually acceptable constructs in individual model development. Organizational interoperability implies an alignment between team processes and procedures. Organizational interoperability for the collaborative team can be established if the models align with a common reference architecture and can be simulated to verify behavior. The
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term "interoperability" is usually reserved for a semiautomated exchange of data and information between networked systems. Therefore we are using the term "compatibility" to refer to the different actions teams must take to refine and share models among themselves. LEVELS OF SYSML COMPATIBILITY Level 1 - Technical Level 1 compatibility, or technical compatibility, makes certain that files can be exchanged and opened by other team members. This means that all teams are running compatible SysML programs. At this stage, the product being exchanged is considered a "picture", i.e. a SysML based graphic. The diagram meets the open and read criteria for the SysML program, however, it may not be a correct use of the SysML language that specifies the modeler’s intentions. An example of this is shown in Figure 1. In this figure, swim lanes are being used to allocate objects in the model to activities, however, the specified objects do not exist in the model. If they did, the objects "PGS" and "MG Team" would be inner swim lanes, i.e. contained in "Squad 2". In order to improve this diagram, and move to Level 2 compatibility, the syntax should be corrected. In this case, the swim lane objects can be replaced with comments if there are no blocks or instances yet specified. Level 1 compatibility ensures that all teams can exchange and open files, but the models are viewed as pictures, rather than software models.
Figure 1. A SysML "Picture"
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Level 2 - Informational (Syntax)
Level 3 - Informational (Semantic)
Level 2 compatibility, or informational (syntax) compatibility, guarantees that all models exchanged are correctly implementing the SysML modeling language. At this level, the diagram is correct and is a useful presentation of stakeholder intentions. It can be used as a common representation for the team to agree on a modeling approach and assumptions, i.e., it can be used to share descriptive data across the teams. At this stage, however, it is still a "picture, and is not yet a computer based implementation of the model. There is still some lack in content to consistently derive meaning of the represented system. An example of this is shown in Figure 2. In this figure, the previous model has been corrected by deleting the swim lanes, as details of these objects are not yet available in model, and replaced with comments to capture the modeler's intent. With these changes the model is syntactically correct, however the comments suggest that there are other elements that need to be included in the model in order to represent the allocation relationships required by the diagram. This level of detail will be necessary before the activities shown can be decomposed into actions necessary for executable detail. In order to implement this as a computer based model, the implied elements and relationships will need to be specified. At the Level 2 compatibility, however, the model is syntactically correct.
Level 3 compatibility, or informational (semantic) compatibility, implies a set of integrated diagrams that compose a complete SysML model. The model is syntactically correct and fully specified; i.e. it includes blocks with specified behavior, properties, relationships and constraints. Figure 3 shows the semantically correct model with structural and behavioral elements; the "fork" shown in the diagram indicates that activities are decomposed into individual actions. Additionally, the model is now supported by a block diagram indicating the required relationships and element properties, as shown in Figure 4. The final improvements required by this model are to add additional details that support execution of the model, for example, triggers and time dependencies for activity diagrams. At Level 3 compatibility, the model can be verified in total for correctness in language syntax and system representation.
Figure 3 - A SysML Activity Model Semantically Correct
Figure 2. A SysML Picture Syntactically Correct
Figure 4. Block Diagram to support the Activity Model
Proceedings of the Human Factors and Ergonomics Society 2016 Annual Meeting
Level 4 - Organizational (Executable) Level 4 compatibility, or an executable model, implies that models at this level can be simulated to verify behavior and validate the expected range of outcomes. It implies that both levels of information compatibility have been achieved (syntactic and semantic) and there is enough detail captured in the model to support simulation. Any team that receives the model at this level can use it to test assumptions about the system. As shown in Figure 5, the "Move Forward" activity is assigned to the "Squad" object, which is further decomposed into activities and actions that invokes both the "Move" and "Update Time" activities. In Figure 6, the "Move" activity, which models soldier movement, is shown. It is an executable model that uses the soldier object's location value and changes it; activities act on object variables changing its state, i.e., location and time. At Level 4 compatibility, the model has complete information and can be executed to verify behavior and constraints.
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FINDINGS A summary of the Levels of SysML Compatibility is shown in Table 1. Level 1 models, with incorrect syntax, require extensive communication between collaborating teams; the model fails to clearly depict the modeler’s intentions and working assumptions. To correct this, simple or familiar SysML constructs should be used and incomplete information can initially be expressed using “comments.” Model exchange should ideally begin from Level 2. Diagrams at this level have incomplete specification but can still communicate what is initially known (and unknown) in a structurally correct manner. Models at Level 3 are fully integrated and represent presentations derived from an underlying structure of interconnected model elements. Ideally the model elements are modular and can be imported or reused across collaborating organizations attempting to model similar concepts. At Level 4 (executable) the model consists of blocks with specified relationships, constraints and behaviors, and can be simulated with consistent results across collaborating organizations.
DISCUSSION
Figure 5. "Move Forward" Activity
Figure 6. "Move" Activity
Model Based System Engineering (MBSE) focuses on capturing system design information using models, and SysML provides a common language to share models between architecting, performance modeling, and engineering teams. Following a MBSE process facilitates integration, reuse and consistency, as well as supports trade-space analysis that allows more complex issues to be explored. However, a common modeling platform and language is not enough to ensure interoperability between multiple modeling teams. Levels of SysML Compatibility were derived as part of the MBSDF initiative to specify best practices between teams and to ensure seamless sharing of information. Using the described levels of compatibility, model and software versions were agreed upon and test files were sent and opened by all teams (Level 1). Models were then improved so that the IMPRINT program could open and manipulate the models with a minimal of analyst interaction (Level 2). Currently efforts are underway to ensure that the architecting models can link to previously developed system engineering models (Level 3). Finally the goal of the program will be to have a set of fully executable models (Level 4).
Proceedings of the Human Factors and Ergonomics Society 2016 Annual Meeting
Table 1. Levels of SysML Model Compatibility Level of Compatibility 1. Technical
Functionality Teams can open and read models exchanged with other teams.
Description
Use of SysML to informally display Model Type = information; syntax Pictures may not be followed and meaning is subject to interpretation. 2. Informational Language Use of SysML to (Syntax) and correctly express standards modelers intentions, Model Type= used with syntax correctly Correct Syntax correctly adhered to, however, Pictures across model still subject to models. reader's interpretation. 3. Informational Models have Use of SysML to (Semantic) shared correctly express meaning, modelers intentions; Model Type= implying diagram is Fully Integrated concepts syntactically correct, Model used all implied blocks uniformly specified, and model across teams. can be instantiated and behavior verified. 4.Organizational Models can Models across teams (Executable) be simulated can be integrated, and across instantiated, and the Model Type= organizations behavior verified. Simulation with Ready expected results.
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ACKNOWLEGEMENTS This work was supported by the Human Research and Engineering Directorate, Army Research Laboratory. REFERENCES INCOSE, 2015. Systems Engineering Handbook, 2015, prepared by the International Council on Systems Engineering (INCOSE), 4th Edition. Friedenthal, S., Moore, A., & Steiner, R. (2015). A Practical Guide to SysML the Systems Modeling Language. Elsevier, Inc. NIST (2010). High Level Reference Model for the Smart Grid developed by National Institute of Standards and Technology (NIST), Handley. H. & Knapp, B. (2014). Where are the people? The human view approach for architecting and acquisition, Defense Acquisition Research Journal, 21(4), 851-874. Mitchell, D. (2009). Workload Analysis of the Crew of the Abrams V2 SEP: Phase I Baseline IMPRINT Model. ARL-TR-5028. Army Research Laboratory
