PSI Suite of Ontologies
PSI Project and Suite of Ontologies
Performance Simulation Initiative (PSI) is the project of Cadence Design Systems GmbH. PSI deals with the development of the methodology and the software toolset for assessing and optimizing the performance of engineering design processes in microelectronic and integrated circuit design. The design technology in this domain is well defined. However, many factors make engineering design processes very stochastic, non-deterministic, structurally ramified, time-bound – in a phrase, loosely defined and highly dynamic. The examples of such factors are: the human factor, the innovative character, the pace of technology change, the peculiarities of the market and the customer requirements, etc. In difference to many alternative and competitive approaches to assessing the performance of engineering design PSI goes deeper in the details of a design system and a process and uses simulation for modeling performance in its real dynamics and with sufficiently detailed picture to make the assessment grounded. To emphasise the focus on dynamics the processes of engineering design in PSI are qualified as Dynamic Engineering Design Process (DEDP). Simulation approach also allows playing “what-if” games to model the unpredictable character of the real business world in the domain.
Due to the omnipresence of the complicating and de-linearizing factors mentioned above the finely grained and complete knowledge of a process is the central intellectual asset which allows the PSI methodology be convincing and produce grounded assessments. This knowledge is formalized using the PSI Suite of Ontologies that forms a logically sound descriptive theory of the domain.
The Structure of the Suite
Indeed, if someone intends to imagine an arbitrary process of designing something, most certainly he or she will think in terms of: a goal – the state of affairs to be reached; an action that may bring the process closer to its goal; an object to apply actions to; a designer who acts and applies actions to objects; an instrument to be used by an actor for executing actions; and an environment surrounding and embedding all the above. All these are modeled in dynamics – depending on time and on events which manifest the changes in a design system that is the environment of a DEDP. The structure of the PSI Suite of Ontologies reflects this approach. It comprises eight Core ontologies: the PSI Core Time ontology; the PSI Core Environment, Event, and Happening ontology (E2H); the PSI Core Actor ontology; the PSI Core Organization ontology; the PSI Core Process Pattern ontology; the PSI Core Process ontology; the PSI Core Design Artifact ontology; and the PSI Core Design Artifact Complexity and Quality ontology (DASpecifc). The “corolla” of this Core is formed by the Extension ontologies. Some of the Extensions have been developed in PSI: The Software Tool Evaluation ontology, the Ability ontology, the Generic Negotiation ontology. The others are the results of the accomplished PRODUKTIV+ project: the Resource ontology, the Library ontology, the Tool ontology. For the ontologies adopted from PRODUKTIV+ we provide ontology mediators that allow us deriving the ongoing development from the knowledge artifacts that have already been accomplished and can not be changed.
The structure of the PSI Suite of Ontologies is presented in the Figure.
The inports are specified in the UML class diagrams of the respective ontologies and in the OWL files. Formally, ontology B imports ontology A (B - - - > A in the Figure) if B specifies the relationships of its own concepts to the concepts of ontology A. It could be stated that ontology B refines the basic model specified in the imported ontology A by specifying these new relationships or by specifying new constraints in the relationships of the imported ontology A. Import relationship both in UML and OWL complies with the law of transitivity:
(B - - - > A) AND (C - - -> B) ≡ (C - - - > A)
The following could be inferred from the map of imports:
- PSI Upper-Level ontology (PSI-ULO) is the most abstract and general theory that is imported by all other ontology modules
For software implementation reasons (complexity) it is allowed not to import the PSI-ULO by the modules of the Core. The OWL of the Core modules is developed in two variants: the one that imports the PSI-ULO and the one that does it not.
- The most abstract module of PSI Core is the PSI Core Time ontology. The model of time is the basic descriptive framework for specifying the Core theory of the domain
- The model of design artifact quality and complexity (the DASpecifc ontology) is static because it does not import the Time ontology. All other models are dynamic
- PSI Suite of Ontologies is based on the dymanic model of representing Environments, Events, and Happenings - PSI Core Environment, Event, and Happening ontology (E2H)
- The mediator Extension ontologies import both the required Core module and the external ontology that is refined and harmonized with the Core by the means of the mediator. By introducing mediators we obtain the way of making required refinements in the external ontologies that can not be changed directly. The external ontologies that are mediated Extensions are: IMS Resource ontology and IMS Tool ontology
- Some external ontologies are used as the Extensions without changes: IMS Library ontology. It is possible because the IMS Library ontology specifies the imports that are required in the PSI Suite of ontologies v.2.3.
The Use of PSI Ontologies
PSI ontologies are used:
- To formally describe the Domain of Discourse – to model Design Systems and DEDPs
- To provide soundly defined unified (standardized) lexicon for Cadence and its customers
- To structure the PSI knowledgebase used in performance assessment experiments
- To derive the specifications of the software tools under development
The major use of the PSI ontologies is the knowledge representation and schema for the assessment of industrial engineering design processes using PSI approach. Consequently the goal of the assessment process is to gradually accumulate the fine-grained knowledge about a design system and performed DEDPs in the phases of Measurement, Simulation, and Evaluation. Each phase adds new pieces of knowledge to the collection acquired at the previous step. This knowledge is formalized using PSI ontologies.
The differences from the Previous Version 2.2
Current version v.2.3 of the PSI Suite of Ontologies differs from v.2.2 as follows:
- The model of design artifact complexity and quality has become the part of the Core as a substantially refined PSI Core Design Artifact Complexity and Quality ontology
- The PSI Core Design Artifact ontology has been extended and refined to incorporate the quality model and the model of requirement- and quality-sensitive states
- The PSI Core Time ontology has been extended and refined to the medium expressivity subset of the PSI Time framework
- The germ of the Organization ontology has been elaborated to a full scale PSI Core Organization ontology comprising some concepts of the former PSI Core Actor ontology and the former PSI Core Project ontology
- The ontology of Events and Happenings has been revised and refined in its environmental part – it now includes the refined model of an Environment and its affected parts as well as the model of a Context
- Some changes have been applied to the Actor, Process Pattern, and Process ontologies to correct noticed mistakes and harmonize them with the rest of the Core
- The rule for ontology imports in the Suite has been made explicit and has been consistently used in shaping out ontology modules and their interrelationships.
Full details about the PSI Suite of Ontologies v.2.3 could be acquired from its Reference Specification.