-The increasing complexity of distributed applications requires new modeling and engineering approaches. Such domains require representing the regulating structures explicitly and independently from the acting components (or agents). Organization computational models, based on Organization Theory, have been advocated to specify such systems. In this paper, we present the organizational modeling approach OperA and a graphical environment for the specification and analysis of organizational models, OperettA. OperA provides an expressive way for defining open organizations distinguishing explicitly between the organizational aims, and the agents who act in it.
The engineering of applications for complex and dynamic domains is an increasingly difficult process. Requirements and functionalities are not fixed a priori, components are not designed nor controlled by a common entity, and unplanned and unspecified changes may occur during runtime. There is a need for representing the regulating structures explicitly and independently from the acting components (or agents). Organization computational models, based on Organization Theory, have been advocated to specify such systems.
Traditionally, Multi-Agent Systems (MAS) stress the
autonomy and encapsulation characteristics of agents. In such
agentcentric view, interactions between agents are mostly seen as
speech acts whose meaning may be described in terms of
the mental states of an agent. As systems grow to include
hundreds or thousands of agents, it is necessary to move
from an agent-centric view of coordination and control to an
organization-centric one. Organizations provide stable means
for coordination that enable the achievement of global goals.
In this sense, organization models play a critical role in the
development of larger and more complex MAS [
Comprehensive analysis of several agent systems has shown
that different design approaches are appropriate for different
domain characteristics [
Models for agent organizations must, on the one hand, be
able to specify global goals and requirements but, on the other
hand, cannot assume that participating actors will always act
according to the needs and expectations of the system design.
Concepts as organizational rules [
The OperA model [
In this paper, we present OperettA, a graphical environment
for the specification, validation and analysis of organizational
models, based on the OperA formalism [
The paper is organized as follows: first, in section II we introduce and briefly explain the OperA framework. In section III the specification of organizational models in OperA is detailed. In section IV we introduce the OperettA Environment. In section V we provide some design guidelines for organization models. Finally, section VI gives our conclusions. II. ORGANIZATION MODELING: THE OPERA FRAMEWORK
Organizational models should enable the explicit
representation of structural and strategic concerns and their adaptation
to environment changes in a way that is independent from the
behavior of the agents. Organization models, combining global
requirements and individual initiative, have been advocated
to specify open systems in dynamic environments [
The deployment of organizations in dynamic and
unpredictable settings brings forth critical issues concerning the
design, implementation and validation of their behavior [
Therefore, organizational models must provide means to represent concepts and relationships in the domain that are rich enough to cover the necessary contexts of agent interaction while keeping in mind the relevance of those concepts for the global aims of the system.
The OperA model [
The OperA framework consists of three interrelated models. The Organizational Model (OM) is the result of the observation and analysis of the domain and describes the desired behavior of the organization, as determined by the organizational stakeholders in terms of objectives, norms, roles, interactions and ontologies. The OM provides the overall organization design that fulfills the stakeholders requirements. Objectives of an organization are achieved through the action of agents, which means that, at each moment, an organization should employ the relevant agents that can make its objectives happen. However, the OM does not specify how to structure groups of agents and constrain their behavior by social rules such that their combined activity will lead to the desired results. The Social Model (SM) maps organizational roles to agents and describes agreements concerning the role enactment and other conditions in social contracts. Finally, the Interaction Model (IM) specifies the interaction agreements between role-enacting agents as interaction contracts. IM specification enable variations to the enactment of interactions between roleenacting agents.
The OperettA framework is developed to specify
organization models, according to the OperA OM, which will be
described in more detail in section III, using as example the
conference organization scenario taken from [
Moreover, organization specification should include the description of concepts holding in the domain, and of expected or required behaviors.Therefore, these structures should be linked with the norms, defined in Normative Structure, and with the ontologies and communication languages defined in the Communication Structure.
The social structure of an organization describes the roles holding in the organization. It consists of a list of role definitions, Roles (including their objectives, rights and requirements), such as PC-member, program chair, author, etc.; a list of role groups’ definitions, Groups; and a Role Dependencies graph.
Abstract society objectives form the basis for the definition of the objectives of roles. Roles are the main element of the Social Structure. From the society perspective, role descriptions should identify the activities and services necessary to achieve society objectives and enable to abstract from the individuals that will eventually perform the role. From the agent perspective, roles specify the expectations of the society with respect to the agent’s activity in the society. In OperA, the definition of a role consists of an identifier, a set of role objectives, possibly sets of sub-objectives per objective, a set of role rights, a set of norms and the type of role. An example of role description is presented in table I.
Id Objectives Sub-objectives Rights Norms & Rules
PC member paper reviewed(Paper,Report) {read(P), report written(P, Rep), review received(Org, P, Rep)} access-confmanager-program(me) PC member is OBLIGED to understand English IF paper assigned THEN PC member is OBLIGED to review paper BEFORE given deadline IF author of paper assigned is colleague THEN PC member is OBLIGED to refuse to review asap
Groups provide means to collectively refer to a set of roles and are used to specify norms that hold for all roles in the group. Groups are defined by means of an identifier, a nonempty set of roles, and group norms. An example of a group in the conference scenario is the organizing team consisting of the roles program chair, local organizer, and general chair.
The distribution of objectives in roles is defined by means of the Role Hierarchy. Different criteria can guide the definition
III. THE ORGANIZATION MODEL of Role Hierarchy. In particular, a role can be refined by A common way to express the objectives of an organization decomposing it in sub-roles that, together, fulfill the objectives is in terms of its expected functionality, that is, what is of the given role. the organization expected to do or produce.In OperA, the This refinement of roles defines Role Dependencies. A Organization Model (OM) specifies the means to achieve such dependency graph represents the dependency relations beobjectives. That is, OM describes the structure and global tween roles. Nodes in the graph are roles in the society. Arcs are labelled with the objectives for which the parent role depends on the child role. Part of the dependency graph for the conference society is displayed in figure 1. For example, the arc between nodes PC-Chair and PC-member represents the dependency between PC-Chair and PC-member concerning paper-reviewed (P C − Chair paper reviewed P C −M ember).The way objective g in a dependency relation r1 g r2 is actually passed between r1 and r2 depends on the coordination type of the society, defined in the Architectural Templates. In OperA, three types of role dependencies are identified: bidding, request and delegation.
organizer role
paper_submitted conference_organized author role PC chair role
PC member
role program _fixed
session_organized paper_reviewed paper_presented session chair role presenter
role
Interaction is structured as a set of meaningful scenes that follow pre-defined abstract scene scripts. Examples of scenes are the registration of participants in a conference, which involves a representative of the organization and a potential participant, or paper review, involving program committee members and the PC chair. A scene script describes a scene by its players (roles), its desired results and the norms regulating the interaction. In the OM, scene scripts are specified according to the requirements of the society. The results of an interaction scene are achieved by the joint activity of the participating roles, through the realization of (sub-) objectives of those roles. A scene script establishes also the desired interaction patterns between roles, that is, a desired combination of the (sub-) objectives of the roles. Table II gives an example of a scene script.
OperA interaction descriptions are declarative, indicating
the global aims of the interaction rather than describing exact
activities in details. Interaction objectives can be more or less
restrictive, giving the agent enacting the role more or less
freedom to decide how to achieve the role objectives and
interpret its norms. Following the ideas of [
PC2 start
Assign deadline
Review deadline end state, that is, landmark patterns actually represent families of protocols. The use of landmarks to describe activity enables the actors to choose the best applicable actions, according to their own goals and capabilities. The relation between scenes is start
SendCal for Participation
Form PC SendCal forPapers
Paper Submission
Registration Review Process
Paper Acceptance
Conference onsite registration
end M Conference
Sessions NWorkshops represented by the Interaction Structure (see figure 3). In this diagram, transitions describe a partial ordering of the scenes, plus eventual synchronization constraints. Note that several scenes can be happening at the same time and one agent can participate in different scenes simultaneously. Transitions also describe the conditions for the creation of a new instance of the scene, and specify the maximum number of scene instances that are allowed simultaneously. Furthermore, the enactment of a role in a scene may have consequences in following scenes. Role evolution relations describe the constraints that hold for the role-enacting agents as they move from scene to scene.
At the highest level of abstraction, norms are the values of a society, in the sense that they define the concepts that are used to determine the value or utility of situations. For the conference organization scenario, the desire to share information and uphold scientific quality can be seen as organization values. However, values do not specify how, when or in which conditions individuals should behave appropriately in any given social setup.
In OperA, norms are specified in the Normative Structure using a deontic logic that is temporal, relativized (in terms of roles and groups) and conditional. For instance, the following norm might hold: “The authors must submit their contributions before the deadline”, which can be formalized as: Oauthor(submit(paper) ≤ Deadline)
Furthermore, in order to check norms and act on possible violations of the norms by the agents within an organization, abstract norms have to be translated into actions and concepts that can be handled within such organizations. To do so, the definition of the abstract norms are iteratively concretized into more concrete norms, and then translated into specific rules, violations and sanctions.
Concrete norms are related to abstract norms through a
mapping function, based on the counts-as operator as developed
in [
Communication mechanisms include both the representation of domain knowledge (what are we talking about) and protocols for communication (how are we talking). Both content and protocol have different meanings at the different levels of abstraction (e.g. while at the abstract level one might talk of disseminate, such action will most probably not be available to agents acting at the implementation level). Specification of communication content is usually realized using ontologies, which are shared conceptualizations of the terms and predicates in a domain. Agent communication languages (ACLs) are the usual means in MAS to describe communicative actions. ACLs are wrapper languages in the sense that they abstract from the content of communication.
In OperA, the Communication Structure describes both the content and the language for communication. The content aspects of communication, or domain knowledge, are specified by Domain Ontologies and Communication Acts define the language for communication, including performatives and protocols.
In order to support developers designing and maintaining organization models, tools are needed that provide an organization-oriented development environment. The requirements for such a development environment are the following. 1) Organizational Design: The tool should provide means for designing organizational models in an ‘intuitive’ manner. The tool should allow users to create and represent organizational structures, define the parties involved in an organization, represent organizational and role objectives, and define the pattern of interactions typically used to reach these objectives. 2) Organizational Verification: The tool should provide verification means and assistance in detecting faults in organizational designs as early as possible, to prevent context design issues from being translated to the other levels of system specification. 3) Ontology Design: The tool should to be able to specify, import, and maintain domain ontologies. Domain ontologies specifying the knowledge for a specific domain of interaction should be able to be represented, existing ontologies containing such information should be able to be included (and provide inputs for organizational concepts, such as role or objective names). Ontologies should be maintainable and updatable. 4) Connectivity to System Level: The output of the organizational design tool is intended for use by system level tools, namely MAS environments and agent programming languages. The output of the tool thus needs to provide easy integration and connection between the organization and system level. 5) User-Friendly GUI: A user-friendly graphical interface is to be provided for users to create and maintain organizational models easily. Help and guidelines are useful for beginners to use the tool. 6) Availability: The tool should be available under open source license and for use by other projects.
We have developed the OperettA development environment as an open-source solution on the basis of these requirements. OperettA enables the specification and verification of OperA OMs, which satisfies requirements 1 and 2. OperettA combines multiple editors into a single package. It provides separate editors on different components of organizational models; i.e., it has different (graphical) editors for each of the main components of an organizational model as defined in the OperA framework. These specialized editors correspond to the OperA OM structures: social, interaction, normative and communicative. The OperettA Ontology Manager enable the specification and import of domain ontologies, as in requirement 3.
The OperettA tool is a combination of tools based on the
Eclipse Modeling Framework (EMF) [
The main element of OperettA is the OperA Meta-Model (see figure 4 for an overview of the tools in OperettA and their functionalities). The meta-model, created with the EMF tools, provides the (structural) definition of what organizational models should look like. This meta-model is extended with the default EMF edit and editor plug-ins to provide model accessors and the basic tree-based editor for the creation and management of OperA models. The basic editor has been extended with graphical interfaces for editing parts of the organization model: the social diagram editor, and the
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Next to the graphical editing extensions, OperettA contains three other plug-ins for additional functionality. The Validation Framework provides an improvement over the default validation of EMF-based tools to provide validation of additional restrictions. An ontology managing plug-in is included as well to allow the ontology developed with OperettA to be exported to OWL, as well as allowing for importing existing ontology into the organization to boot-strap the organization design. Finally, OperettA contains a Model Tracker plug-in that can generate re-organization descriptions based on changes made in the OperettA organization editors.
We discuss the graphical editors and additional plug-ins in more details in the following.
1) Social Diagram Editor: This graphical editor provides a view of the Social Structure element of OMs. It allows the graphical creation of organizational Roles and Dependencies, thus specifying the social relations between important parties that play a part in the organization. The Social Diagram Editor also provides editing capabilities to specify and manage Role related Objectives, to provide context for the different Roles in an organization. Figure 5 depicts the Social Diagram Editor of OperettA that is used to enter organizational roles and dependencies between roles. Role objectives are created and managed via the objectives editor shown in the bottom part of the figure.
agram Editor, the Interaction Diagram Editor provides a graphical view of the Interaction Structure element of OMs.
This editor allows for the specification and management of the interaction elements of the organization; that is, it is for the specification and management of the different interactions that take place in the organization in order to achieve the different (role) objectives specified in the social part of the OM. The specification of the interaction is done in terms of scenes and transitions (the connection and synchronization points between scenes). Together, these define the order in which objectives are to be reached and how the organization works (though specified on a high level of abstraction). The Interaction Diagram Editor allows for the graphical creation and maintenance of scenes, transitions and arcs (links between scenes and transitions). The graphical editor provides a userfriendly overview of the structural aspect of the organization, defining how different interactions within the organization are supposed to help achieve the organizational objectives. Finally, OperettA allows for the specification and editing of scene properties (like the scene results, the players active in the scene, the landmark pattern, etc).
3) Ontology Manager: The Ontology Manager part of the OperettA tool is a plug-in for importing and exporting (domain) ontologies. The creation and maintenance of ontologies is done by external tools (like, for example, Prote´ge´). Parts of the functionality of organizational ontology editing is included in the OperettA editors: • Automatic creation of organizational ontology while designing the organization. As the designer is inputting the organizational model in OperettA, OperettA maintains an ontology of role names, objective names, and logical atoms that the designer uses to define the organization. • Using an included (existing) ontology for the naming of organizational model elements; that is, if an (external) ontology is present in the organizational model it can be used to pick concept names for different parts of an organizational model (e.g., the name of a role can be picked from an existing ontology included in the model). The addition of the (external) ontology to an organizational model is done via the ontology manager.
The functionality of ontology editing in the OperettA tools
is limited to organizational ontologies. The Ontology manager
plug-in extends OperettA with the following capabilities:
• Importing an ontology from a file (e.g., RDF or OWL
[
The organizational ontology created by OperettA is stored in the Organizational Model. The ontological elements need to be available to the system level of design, and thus need to be included in the domain ontology. The integration of organizational concepts in a domain ontology is not trivial, as it should respect the structure of the domain ontology while adding organizational concepts as roles, objectives, etc. and the instances of these concepts; role names, objective names, etc.
The alignment between the exported ontology and the domain ontology will have to be done by hand in an external editor.
The inclusion of the ontology manager satisfies requirement 3.
6) Norm Editor: Norms are an important part of the organizational Model, providing lead ways on a high level of abstraction for the agents to follow. Norms can be inputted in the current version of OperettA via the basic EMF generated editor. This editor is not user-friendly. An example norm in OperettA is shown below in figure 6. The norm shown in this figure describes that buyers should have paid for the items they have won in an auction before one week has expired.
The norm is input using several logical formulas; one for the activation condition expressing when the norm is active 4) Model Tracker: To support reorganization, OperettA is (the item is bid on and won), one for the expiration condition extended with a model tracker. This model tracker allows a expressing that the norm is no longer active (the item has designer to view the changes made on the organizational model been paid for), one for the maintenance condition expressing since a last save (but not necessarily the previous one). By the formula to be checked when the norm is active to see if storing the changes to the organizational model in a history violations have happened (the buyer has not paid and the week file, the model tracker can be used to generate scripts that has not yet expired), and one for the deadline expressing a state express how an organization is changed. Reorganization scripts of affairs before which the norm should have been fulfilled. A capture changes in a precise and concise manner, and can user-friendlier (graphical) interface for inputting and managing be used to communicate organizational changes to the system the norms of an organizational model is planned for a future level. version of OperettA. This extension, with the graphical editors 5) Validation Framework: The validation plug-in of Op- for the social and interaction structures, fulfills requirement 5. erettA overwrites the basic validation provided by the EMF framework. Instead of just verifying constraints specified in B. Connectivity to System Level the OperA meta-model, the validation has been extended with The OperettA tool has only off-line functionalities; it is additional verification constraints to minimize organizational used by designers to create the context of the system and design mistakes. The overall purpose of the validation plug-in their linked ontologies. It provides design and validation is to provide OM designers meaningful feedback to eliminate functionalities for the creation and management of OperA design errors as early as possible (in the design process). organizational models. For the connection to implementations The validation plug-in is installed separately from OperettA, OperettA depends on the Model Driven Engineering (MDE) but after installation it can be invoked from within each of approach by providing a meta-model of the modeling concepts. the different OperettA editing views. The validation plug-in MDE refers to the systematic use of models as primary seamlessly overwrites the standard EMF validation, making it artifacts throughout the Software Engineering lifecycle. The the new default manner of validating OperettA models. defining characteristics of MDE is the use of models to
The validation plug-in works directly on the model instance represent the important aspect of the system, be it requireto verify various modeling constraints, accessing the model via ments, high-level designs, user data structures, views, interopthe meta-model definitions. Some examples of the constraints erability interfaces, test cases, or implementation-level artifacts validated are checking that roles have a name, checking such as code. The Model Driven Development promotes the that role names are unique, checking that all roles have an automatic transformation of abstracted models into specific objective, and so on. Less stringent constraints are checked as implementation technologies, by a series of predefined model well, like, for example, whether roles are connected to other transformations. roles via dependencies; i.e., while it does not hold for every In essence, this means that the models created with the OM, in most models roles should be connected to other roles OperettA tool can be used for automated transformation (that is, it should be depending upon (an)other role(s) or being towards applicable (models of) platforms; e.g, service-based depended upon by (an)other role(s)). Such “soft” constraints implementations or multiagent systems. The only required step are presented to designer as a warning, intended to have the for such transformation is the definition of the transformations designer rethink their model and update if appropriate. The based on the OperettA meta-model concepts to the meta-model validation plugin fulfills requirement 3. of the desired platform.
Finally, OperettA is based on the OperA formalism, which
assumes that individual agents are designed independently
from the organization, to model goals and capabilities of a
given entity. Individual agents are the enactors of
organizational role(s), as a means to realize their own goals [
In the previous we introduced organizational modeling and
the OperettA Environment to support this. In this section we
present a small overview on how one goes about designing an
organization. After identifying that an organization presents
the solution to the problem:
1) Identify (functional) requirements: First one determines
the global functionalities and objectives of the society.
2) Identify stakeholders: The analysis of the objectives of
the stakeholders identifies the operational roles in the
society. These first two steps set the basis of the social
structure of the OperA model.
3) Set social norms, define normative expectations: The
analysis of the requirements and characteristics of the
domain results in the specification of the normative
characteristics of the society. This results in the norms
in the normative structure.
4) Refine behavior: Using means-end and contribution
analysis, a match can be made between what roles
should provide and what roles can provide. This aspect
contributes to refinement of role objectives and rights.
5) Create interaction scripts: Using the results from steps 3
and 4, one can now specify the patterns of interaction for
the organization, resulting in the interaction structure.
More details about the methodological steps taken to create
organizational models can be found in [
In this paper, we present an organization-oriented
modeling approach for system development. The OperA modeling
framework can be used for different types of domains from
closed to open environments and takes into consideration
the differences between global and individual concerns. The
OperettA tool supports software and services engineering
based on the OperA modeling framework. It has been used in
the European project ALIVE [