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Overview

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Opportunities and Challenges for Deep Constraint Languages

Colin AtkinsonRalph GerbigThomas Kühne

Ottawa, Camada28 September, 2015

OCL 1015@MODELS 2015

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The Challenge

■ Structural models (e.g. in UML) are often augmented with (additional) constraints (e.g. in OCL) to rule out unwanted instance configurations

■ Constraints add further requirements that (token) models (instances) must obey to be considered instances of their (type) model■ provide additional well-formedness requirements■ rule out unwanted configurations of instances■ improve the precision of the semantics of the type model

■ Today’s constraint languages are designed to support traditional “two-level” modeling languages and thus assume that constraints -■ are attached to types and evaluated on their instances■ are implicitly universally-quantified, i.e., use a “for-all”-semantics ■ have only one instance level to control, i.e., deep control beyond

more than one classification boundary is not possible

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Goals

■ the goal of this paper is to ■ re-evaluate the role of constraints for deep modeling■ identify di erent kinds of constraints possible on deep modelsff■ establish terminology for referring to them■ explore what language features might be useful

■ It is NOT the goal of the paper to■ resolve all tradeoffs necessary in the design of a Deep

Constraint Languages (DCLs)■ propose specific concrete syntax for DCLs■ present a complete, fully thought out DCL

■ The focus is exclusively on ■ structural modeling■ contraint languages

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Deep Modeling

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Realization Strategy 1

■ Make the linguistic (meta) model the tool meta-model and add support for ontological classification at the “instance” level

Ecore

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Realzation Strategy 2

■ Transformation chains between “two-level” windows

Tool 1

Tool 2

Transformations

…

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Opportunities and Challenges for DCLs

■ The features of deep modeling that present the biggest opportunities and challenges from the perspective of defining constraints are■ the two distinct, orthogonal classification dimensions■ dual facets of model elements (i.e. the existence of linguistic

and ontological attributes)■ an unbounded number of ontological classification levels.

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Linguistic Constraint Example 1

■ The value of the potency of every clabject must be one lower than that of its direct type

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Linguistic Constraint Example 2

■ The value of the potency and level of every clabject must be equal

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Linguistic Constraint Example 3

■ The number of levels in a deep model must be 3

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More General Forms of Constraints

■ Linguistic constraints ■ reference concepts in terms of linguistic types and therefore

have no knowledge of any ontological types

■ Ontological constraints■ operate within level L0 to express well-formedness conditions

on the content of ontological levels■ access ontological attributes and model information■ have more than one immediate instance level to constrain

■ Universal “for-all” at the immediate level below is no longer optimal■ need a more general form for constraints

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Ontological Constraint Example 1

■ the constraints that end users (i.e. modellers) write in conventional modeling environments are typically ontological constraints

■ The value of a ProductType’s price attribute has to be smaller than or equal to its RRP attribute

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Hybrid Constraints

■ Limiting constraints to operating in just the linguistic dimension or the ontological dimension (but not both) is too restrictive ■ need to allow statements about both forms of instantiation to be

mixed (i.e. need hybrid constraints)

■ But how should ambiguities (i.e. name clashes) be avoided?

a) rule out the use of linguistic model names in the ontological levels (i.e. in the domain content)

b) provide a special syntax for selecting between linguistic and ontological elements

c) introduce default rules based on the “location” of the constraint

d) support some mixture of (b) and (c)

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Example Hybrid Constraint

■ The (default) prices for instances of CarType, and their instances, must be greater than zero

(DeepOCL)

(Metadepth)

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Deep Constraints

■ may target one or more levels somewhere below the origin clabject

■ Instances versus offspring■ instances of a clabject exist at the level immediately below that

clabject, and can be direct or indirect instances■ o spring of a clabject are all clabjects in the transitive closure ff

of the “classifies” relationship starting with that clabject

■ constraints can be level-specific or level-spanning■ level-specific constraints restrict the properties of clabjects to

one specific level relative to the origin clabject■ they have a SCOPE of 1

■ level-spanning constraints restrict the properties of clabjects to a range of levels relative to the origin clabject■ they have a SCOPE of greater than 1

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Level-Specific Constraints

■ Constrain the clabjects at one specific level relative to the origin clabject

■ can either be -■ Inter-level

■ constrain some arbitrary, specified level containing offspring of the origin clabject

■ constrain the lowest level containing o spring of the origin ffclabject

■ Intra-level■ constrain the level containing the origin clabject element itself

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Inter-Level Constraint Example 1

■ The recommended retail price of a CarType must be between 10k and 400k

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Inter-Level Constraint Example 2

■ The price actually paid for a car shall be no more than 80% of the recommended retail price

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Intra-Level Constraint Example 1

■ Subtypes of Car with potency higher than 0 must be instances of CarType (cf. PowerType Pattern)

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Intra-Level Constraint Example 2

■ Subtypes of Car with potency higher than 0 must add attributes

origin (0) Car

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Level-Spanning Constraints

■ Constrain the clabjects in a specific range of levels relative to the origin clabject

■ can either be -■ all offspring of the origin clabject in a specified range of levels

below that clabject■ all offspring of the clabject as well as the clabject itself

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Level-Spanning Constraint Example 1

■ All o spring of wheelTypes, over two levels immediately below it, are ffnot allowed to be older than 24 months

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Level-Spanning Constraints

■ The (default-) price for a car must exceed 10000

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“Advanced” Constraint Example

■ The wheels of Dragsters are not allowed to be older than 7 months

■ Clabject-specific but “type” aware

(DeepOCL)

(Hybrid)(MODELS 2015)

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Conclusion

■ The paper explored the different kinds of constraints that make sense in deep modeling and proposed terminology for referring to them■ the taxonomy is not necessarily mutually exclusive

■ In the context of deep modeling it is possible to write kinds of constraints that cannot be specified in SCLs, such as ■ hybrid constraints

■ deep constraints

■ intra-level constraints

■ we do not use higher-order constraints (constraints on constraints) like other approaches that try to support the effects of hybrid constraints

■ some of these ideas have been implemented in existing deep modeling environments such as ■ Metadepth, DeepOCL (available in Melanee)

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That’s It

Thank you for your attention