SEQUAL — Semiotic Quality Framework

A theoretically-grounded framework for evaluating conceptual-model quality based on semiotic correspondences between sets. Originally proposed by Lindland, Sindre, Sølvberg (1994) with three quality levels (syntactic, semantic, pragmatic), later extended by Krogstie et al. to cover all eight levels of Stamper's semiotic ladder, and revised by Krogstie, Sindre & Jørgensen (2006) for active process models.

The set-correspondence apparatus

Quality is defined as correspondence between sets of statements:

Set	Meaning
G	modelling goals — what the model should achieve
L	language extension — everything expressible in the chosen modelling language
D	modelling domain — everything that can be said about the situation at hand
M	externalised model — the actual model artefact
K_s	social-actor explicit knowledge
K_m	modeller explicit knowledge
I	social-actor interpretation of M
T	technical-actor interpretation of M (e.g., what software does with the model)

Quality types are correspondences between these sets (mapped to Stamper's semiotic ladder):

Quality type	Correspondence	Goal
Physical	externalisation + internalisation of M	Model is available, accessible
Empirical	M readability	Layout, comprehensibility heuristics
Syntactic	M ⊆ L	Syntactic correctness
Semantic	M vs D	Validity (M ⊆ D, no false statements) + Completeness (D ⊆ M, no missing)
Perceived semantic	I vs K_s	Perceived validity + perceived completeness
Pragmatic	M vs (I, T)	Comprehension by interpreters
Social	agreement among I's	Feasible agreement
Organisational	M fulfilling G	Goal fulfilment

Feasibility — why absolute quality is unattainable

Validity (M ⊆ D) and completeness (D ⊆ M) are typically infeasible in absolute terms — D is too large to know fully, and modelling has finite cost. SEQUAL introduces feasibility so modelling can terminate when further effort yields less benefit than acceptance. Practical quality is therefore feasible validity and feasible completeness.

The 2006 revision (Krogstie, Sindre & Jørgensen)

sources/2006-krogstie-sindre-jorgensen-revised-sequal-framework reframes SEQUAL for active process models — models that don't merely describe reality but actively change it through enactment. Three shortcomings motivate the revision:

Static D: original SEQUAL treats domain as given; active models change D.
Narrow pragmatic quality: limited to comprehension where modern semiotics emphasises interpreter impact (action).
Knowledge-as-object framing: original treats models as externalised knowledge; revised view (Polanyi-aligned) treats knowledge as in-mind, with models as supports.

New sets

D^O — optimal domain (the situation the organisation would or should want).
K^N — knowledge need (what knowledge the organisation needs).

Three semantic-quality flavours in revised SEQUAL

Type	Correspondence	Used for
Descriptive semantic quality	M vs D	as-is models — does the model match current reality?
Prescriptive semantic quality	M vs D^O	to-be models — does the model match desired reality?
Semantic quality (formerly "perceived semantic")	K vs M	does the model fit actual stakeholder knowledge?

Articulation / activation dynamic

Articulation (D → M): capturing domain in the model. Manual (human modeller) or automatic (sensors, log mining).
Activation (M → D): model-guided action transforming the domain. Manual (human reads model and acts), automatic (workflow engine interprets), interactive (mixed).

The interplay produces co-evolution between model and domain — the dynamic engine of active modelling.

Pragmatic quality redefined

Comprehension is necessary but not sufficient. The revised pragmatic quality requires:

Learning: ΔK ∩ K^N (model contributes to filling the knowledge gap).
Action: ΔD toward D^O (model-driven changes move the domain toward the optimum).

This is a more demanding criterion suited to active and interactive process models.

Where SEQUAL appears in BPM literature

sources/2018-dumas-fundamentals-of-bpm §5.4 distils SEQUAL into a three-aspect tripartite (syntactic / semantic / pragmatic) — more actionable for textbook readers but a simplification of the eight-level scheme.
sources/2010-mendling-reijers-vanderaalst-7pmg explicitly positions itself against SEQUAL: critiques SEQUAL as "too abstract to be applicable for novices and non-experts" and proposes 7PMG as the operational complement targeting (primarily) pragmatic quality.

Strengths

Theoretical scaffolding for what model quality even means — rooted in semiotics rather than ad hoc engineering checklists.
Decoupling of dimensions — physical/empirical/syntactic/semantic/pragmatic/social/organisational are orthogonal — a model can be sound but socially unaccepted, or comprehensible but goal-misaligned.
As-is vs to-be distinction in the revised version maps directly to BPM lifecycle phases: discovery (descriptive) → redesign (prescriptive).
Anticipates active/agentic systems — the activation concept prefigures agentic-BPM execution.

Limitations (acknowledged by authors)

Qualitative, not quantitative — SEQUAL structures evaluation but does not yield a numeric score. Krogstie et al. note this is the disability the revision does not fix.
Operationalisation gap: only syntactic quality has hope of objective measurement; semantic and pragmatic quality involve unknowable sets.
Practitioner accessibility: the framework is too abstract for non-experts to apply directly — hence 7PMG and similar operational distillations.

Relationship to other quality concepts

Layer	Concept	Role
Theoretical scaffold	SEQUAL	Defines what quality dimensions exist
Textbook tripartite	concepts/process-model-quality	Distillation of SEQUAL into 3 actionable buckets
Operational toolkit	concepts/7pmg	7 concrete rules targeting (mostly) pragmatic quality
Bottom-up metrics	concepts/process-model-complexity-metrics	Quantitative measures (size, density, CFC) feeding into pragmatic-quality assessment
Formal correctness	concepts/soundness	Behavioural/structural property — sits inside syntactic-quality bucket
Runtime conformance	concepts/conformance-checking	Model-vs-log dimensions (fitness, precision, generalisation, simplicity) — separate axis

concepts/process-model-quality · concepts/7pmg · concepts/soundness · concepts/process-model-complexity-metrics · concepts/agentic-bpm (active models prefigure agentic execution) · concepts/agent-process-observability (articulation/activation = read/write loop)

Sources

sources/2006-krogstie-sindre-jorgensen-revised-sequal-framework (primary, revised version) · sources/2018-dumas-fundamentals-of-bpm (textbook citation)