Model-Based Development and Evolution of Information Systems

ion . An abstraction is the phenomenon of a set of phenomena and its properties at some level of approximation. The abstraction contains incomplete explicit knowledge about the phenomena, i.e. there are more that can be known about the phenomena than is covered in the abstraction. This does not mean that the abstraction cannot contain all relevant knowledge in a given time interval. Classi fi cation . The abstraction where individual phenomena are grouped together in a class based on perceived common properties. Example: ‘Rod Stewart’ and ‘Mick Jagger’ can be grouped together in the class ‘singers’. Aggregation . An abstraction that is a Cartesian product of classes. For example, a bicycle being built up from wheels, a seat, a frame, handlebars, etc. Generalisation . An abstraction that is a subset of the union of a set of classes. For example, both employees and customers are persons. Association . An abstraction that is a set of classes. For example, the classes ‘Men’ and ‘Women’ are members of the set ‘sex-groups’. Model . A model is an abstraction externalised in a professional language. A model is assumed to be simpler than, resemble, and have the same structure and way of functioning as the phenomena it represents. Conceptual model . A model of a domain made in a formal or semi-formal language with a limited vocabulary. Comment: Many conceptual modelling languages are partly diagrammatic, in which case they are combination of logographic and iconographic symbols, but this is not looked upon as a requirement. Some conceptual modelling languages also have aspects that are pictographic. Language model . The model of a language. Within conceptual modelling, this is often termed ‘meta-model’, which is only a proper term when looking upon it from the point of view of repository-management for a modelling tool where the instantiation of the model is another model in the same or a different modelling language. System model . A model of a system. 415 Appendix A: Terminology A.6 Actors and Activities A phenomenon is acted upon by another phenomenon if its history is different from what it would have been if the other phenomenon did not in fl uence it. Actor . An actor is a phenomenon that acts upon another phenomenon, the actand . Acquaintances . The acquaintances of an actor are the set of actors that either acts upon or is acted upon by the actor. Social actor . A social actor is an actor that includes at least one person. Social actors might be individual or organisational (see below). Technical actor . A technical actor is an actor that does not include any persons. Technical actors can be computational and temporal. Other subtypes of actors might for instance be production actors, but these will not be discussed here. Whereas temporal actors are some time-measuring device (i.e. a clock of some sort), computational actors are either hardware actors or software actors. Computational actors are either atomic or systemic including atomic and systemic subsystems. Computational actors can be said to be compatible in the following meanings: Hardware compatibility: Stating which hardware actors that can act upon each • other. Executional compatibility: Describe which software actors that can be executed on • which hardware actors. Software compatibility: Stating which software actors that can act upon each • other. Software actors can be versions of 0:N other software actors, i.e. a software actor can be recreated by performing a set of state changes to the actor it is a version of. A set of state changes in this meaning are called a delta. The original actor is called a predecessor of the version actor, whereas this is called a successor of the original actor. Software actors might have several predecessors and successors. These relations are transitive. Two or more software actors that have the same immediate predecessor are termed variants. Internal actor . Actors being internal to an organisation are actors being part of the organisational system of the organisation in one or more of the relevant roles they are currently fi lling. External actor . Actors being external to an organisation are actors not being part of the organisational system of the organisation in any of the relevant roles they are currently fi lling. Individual social actor . A person interacting with his environment is termed an individual social actor. We will use the term person synonymously with the term individual social actor . 416 Appendix A: Terminology Organisational social actor . An organisational actor is a social actor that consists of a set of more than one person performing goal-oriented and co-ordinated action. An organisational actor can also include technical actors, but this is not mandatory. Permanent organisational actor . An organisational actor for which a begin time-point of its existence can be perceived, but normally not the future end time-point. Temporary organisational actor . An organisational actor for which both the begin time-point and the possibly future end time-point of its existence can be perceived. Periodic organisational actor . An organisational actor for which a set of begin time-points and (possibly future) end time-points of its existence can be perceived, and where there is normally the same time-interval between the different begin time-points. The duration of this time-interval is longer than the individual lifetime of the organisational actor. Action . An action is the phenomenon of one phenomenon acting upon other phenomena. Activity . An activity is a system of actions. Stakeholder . The stakeholders of an activity are the set of persons who perceive or are perceived by other persons to potentially lose or gain from the activity. Participant . The participants of an activity are the set of persons who act upon the actands of the activity as part of the activity. Process . A process is an activity that takes a set of phenomena and transforms them into a possibly empty set of phenomena. Role . Actions that can be expected by an actor or by other actors. Agent . An actor acting in a particular role. Formal role . A role where part of the expected actions of an actor fi lling the role is institutionalised by an organisational actor. A typical example of a formal role is a position such as a professor. All roles usually also have two additional aspects: The informal part of the role. Expectations to an actor fi lling the role that are not • institutionalised. For example, ‘a professor is absent-minded’. The expectation to an agent, because of the particular actor fi lling the role. • Role con fl ict . Inconsistent expectations to an actor because of fi lling two or more roles in the same time interval or because of differing expectations to a role that the actor fi ll from two or more other actors. 417 Appendix A: Terminology