# Design proposal critique for structural elements

_Exported on 3/9/2026 at 15:13:01 EDT from Cursor (2.6.14)_

---

**User**

This chat is a design discussion that will serve as input to a new decision record (@docs/dev/decision-records/AGENTS.md). You MUST NOT reply with the content of a new decision record as we are not yet writing it.

Critique the following design proposal: All structural elements defined within `rdflib-reasoning-axioms` should be part of a pydantic class hierarchy so that their schema is exposed to `rdflib-reasoning-middleware`. Structural elements MUST NOT contain `rdflib.Graph` objects or any other complex third-party data structures. They MUST extend `rdflib_reasoning.axiom.structural_element.GraphBacked` to declare the graph that they are associated with. Related structural elements MUST have the same `GraphBacked.context`. Structural elements MUST ensure that their generated JSON Schema is terse and optimized  for guidance of an AI/Agent. Structural elements MUST validate their fields and yield error messages that are guidance supporting correction of the error by an AI/Agent or Human. The primary motivator is that Structural elements are REQUIRED to support @rdflib-reasoning-middleware implementations and best practices laid out in <https://docs.langchain.com/oss/python/langchain/middleware/custom> .

1. Are there clear principles that are being established?
2. Is this proposal consistent with the rest of the documentation in the repository (development docs and `README.md`'s)?
3. Are there significant oversights or ambiguities that we should clarify before this can be converted into a decision record?

---

**Cursor**

I’ll first inspect the existing structural element definitions, relevant docs, and middleware README so I can judge consistency and spot ambiguities. Then I’ll walk through your three questions with concrete, pointed feedback and suggested clarifications.

### 1. Are clear principles being established?

**Yes, there are clear, coherent principles emerging, but they’re not all explicit yet.** Implicitly, the proposal (plus current code in `structural_element.py`) is establishing:

- **Agent-first data modeling**
  - Structural elements are **Pydantic models** whose schemas and validation errors are designed to be consumed by agents (LangChain/DeepAgents).
  - This aligns well with the root `README.md` statement that packages “depend on Pydantic for agent-friendly data structures.”

- **Separation of concerns: data vs. graph**
  - Structural elements **MUST NOT embed `rdflib.Graph` or other complex runtime structures**; they expose only identifiers and small rdflib node types (`IdentifiedNode`, `URIRef`, etc.).
  - They **MUST extend `GraphBacked`** and carry only a graph/context identifier (`ContextIdentifier`) rather than a graph instance. That is already consistent with:

    ```12:20:rdflib-reasoning-axioms/src/rdflib_reasoning/axiom/structural_element.py
    class GraphBacked(BaseModel, ABC):
        """An entity that MUST be associated with a specific graph (context)."""

        context: ContextIdentifier = Field(
            ..., description="The graph (context) wherein this entity MUST bedefined."
        )
    ```

- **Context-based scoping**
  - Every structural element explicitly declares the **context/graph** in which its facts apply, and **“related” elements share a context**.
  - This is a strong and useful invariant for middleware and state-tracking, but “related” is not defined yet (see ambiguities below).

- **Explicit, spec-aligned structural modeling**
  - `StructuralElement` and `Seq[T: StructuralElement]` encode OWL 2 structural specification elements and RDF `rdf:List` structure without hiding behavior in a graph:

    ```20:44:rdflib-reasoning-axioms/src/rdflib_reasoning/axiom/structural_element.py
    class StructuralElement(GraphBacked, ABC):
        """An Element of the OWL 2 Structural Specification; Concrete class names SHOULD match the paired structural element's name (e.g., ` NegativeDataPropertyAssertion`)."""

        @abstractmethod
        @property
        def name(self) -> IdentifiedNode:
            ...

        @abstractmethod
        @property
        def as_triples(self) -> Sequence[Triple]:
            """The triples that represent this element as RDF (MUST NOT recurse into related elements)."""
            ...
    ```

- **Validation and error messaging as first-class, agent-oriented API**
  - The `Seq` validator already demonstrates **strong invariants + natural language error messages**:

    ```69:86:rdflib-reasoning-axioms/src/rdflib_reasoning/axiom/structural_element.py
    @model_validator(mode="after")
    def check_list_integrity(self) -> Self:
        if len(self.names) != len(self.elements):
            raise ValueError(
                f"The number of names ({len(self.names)}) and elements ({len(self.elements)}) MUST match."
            )
        if any(name == RDF.nil for name in self.names):
            raise ValueError("The `rdf:nil` node MUST NOT be used as a list head.")
        if len(set(self.names)) != len(self.names):
            ...
    ```

  - Your proposal extends this into an explicit principle: **error messages are guidance for AI/Humans to correct input**, not just diagnostics.

- **Middleware-facing schema as an explicit requirement**
  - You’re explicitly tying structural elements to **LangChain custom middleware** contracts and patterns from `[Custom middleware](https://docs.langchain.com/oss/python/langchain/middleware/custom)`, i.e.:
    - Pydantic schemas as state / tool argument models
    - JSON Schema driving validation and guidance
    - Compatibility with `AgentState`-style extensions and hooks

**Suggested improvement:** I’d make these into explicit bullets in the eventual DR (even if not yet written): “Agent-oriented schema,” “No embedded graphs,” “Context-scoped structural elements,” “Spec-aligned OWL 2 modeling,” and “Middleware-consumable JSON Schema + error semantics.” Right now they’re mostly implied.

---

### 2. Consistency with existing docs / README’s

**Broadly, this proposal is consistent with the existing documentation and direction of the repo.** In some ways it just formalizes patterns you’ve already started:

- **Root `README.md` and architecture**
  - The root `README.md` explicitly calls out that packages:

    ```7:10:README.md
    ... depend on [RDFLib](https://github.com/RDFLib/rdflib) for semantic web support and on [Pydantic](https://docs.pydantic.dev/latest/) for agent-friendly data structures.
    ```

  - Your proposal leans into that: structural elements as **Pydantic-based, agent-friendly data structures** is exactly on-message.
  - The architecture diagram also positions `rdflib-reasoning-middleware` as a supporting package in the LangChain/DeepAgents ecosystem, which matches your motivation to align structural elements with LangChain middleware ([docs](https://docs.langchain.com/oss/python/langchain/middleware/custom)).

- **`AGENTS.md` in the repo root**
  - It establishes that:
    - This repo **MUST support research into agents and interoperability with formal logic**.
    - Pydantic and src-layout & namespace packages are standard.
  - Your proposal strengthens the “interoperability with agents” story by making **structural elements the canonical, schema-based interface** to the axioms package for middleware.

- **`rdflib-reasoning-axioms/AGENTS.md`**
  - That document defines the axioms package as primarily about **round-trip `graph -> axiomatization -> graph`**, and requires adherence to OWL2 mapping specs.
  - Structural elements as Pydantic models that:
    - Encode OWL 2 structural spec elements
    - Provide `as_triples` for graph reconstruction
    - Treat inputs as immutable and produce new outputs
  - …is completely aligned with this; there’s no contradiction, and it clarifies the _internal_ representation used for axiomatization.

- **`rdflib-reasoning-middleware/README.md`**
  - Currently minimal, but it states:

    ```1:3:rdflib-reasoning-middleware/README.md
    This package exposes this repository's functionality to DeepAgents as [Custom Middleware](https://docs.langchain.com/oss/python/langchain/middleware/custom).
    ```

  - Your proposal is exactly the missing piece: **what is the “functionality” that the middleware exposes?** Answer: agent-oriented Pydantic models of structural elements, with JSON Schema + validation tuned for middleware hooks (e.g., `AgentState`, `before_model`, `wrap_model_call`).

- **Docs style and RFC 2119**
  - The docs already emphasize:
    - RFC 2119 terms
    - Optimization for agent understanding (`docs/dev/AGENTS.md`)
  - Your proposal uses RFC 2119 language and focuses on agent guidance—so stylistically and semantically it’s in line.

**Net: the proposal is consistent; it mostly makes existing implicit assumptions concrete, especially the Pydantic/agent-centric design.**

---

### 3. Significant oversights or ambiguities to clarify

There are a few important areas that would benefit from clarification or tightening before you turn this into a decision record.

#### 3.1. Scope and hierarchy of “structural elements”

- **Ambiguity:** “All structural elements defined within `rdflib-reasoning-axioms` should be part of a pydantic class hierarchy.”
  - Do you mean:
    - **All classes representing OWL 2 Structural Specification elements MUST subclass `StructuralElement`**, or
    - _Any_ data model in this package MUST be a Pydantic model?
  - Also, is `StructuralElement` the universal base, or is it acceptable for some things to just be `GraphBacked` but not structural per OWL 2?

**Suggestion:** State explicitly something like:

- “Every OWL 2 structural element represented in this package MUST subclass `StructuralElement`.”
- “Other internal helper models MAY be Pydantic but are NOT considered ‘structural elements’ unless they inherit from `StructuralElement`.”

#### 3.2. What counts as “complex third-party data structures”?

- You explicitly forbid `rdflib.Graph` and “any other complex third-party data structures.”
- Current code already uses rdflib node classes (`IdentifiedNode`, `URIRef`, `Node`) in types:

  ```4:16:rdflib-reasoning-axioms/src/rdflib_reasoning/axiom/common.py
  from rdflib import IdentifiedNode, Node, URIRef
  ...
  type Triple = Annotated[
      tuple[IdentifiedNode, URIRef, Node],
      Field(..., description="A triple of a subject, predicate, and object; i.e., a fact.")
  ]
  ```

- That’s a reasonable boundary: allow lightweight identifiers / terms; forbid heavyweight containers (`Graph`, `ConjunctiveGraph`, query results, etc).

**Suggestion:** Make this boundary explicit:

- E.g. “Structural elements MAY use `rdflib` node/identifier types (`URIRef`, `BNode`, `Literal`, `IdentifiedNode`) and other _atomic_ types, but MUST NOT contain `rdflib.Graph` or any container-like or contextful third-party objects (e.g., SPARQL results, session handles).”

#### 3.3. Semantics of `GraphBacked.context` and “related structural elements”

- You say:
  - “They MUST extend `GraphBacked` to declare the graph they are associated with.”
  - “Related structural elements MUST have the same `GraphBacked.context`.”

Ambiguities/questions:

- Is `context` **always a single graph IRI / identifier**, or might you later support quads / multiple contexts?
- “Related” could mean:
  - Elements appearing together in a `Seq` (list membership)
  - Elements that reference each other’s `name`
  - Elements that are part of the same higher-level construct (e.g., ontology)
- For some use cases, you may _want_ cross-context relationships (e.g. referencing individuals defined in a shared graph from another graph).

**Suggestion:**

- Define “related” operationally, e.g.:
  - “If a structural element `A` directly embeds or references another structural element `B` via a field (not via `as_triples`), then `A.context` and `B.context` MUST be identical.”
- Also, be explicit whether cross-graph references are:
  - Forbidden, or
  - Expressed only at the triple level (`as_triples`) rather than via structural-element embedding.

#### 3.4. JSON Schema requirements: “terse and optimized for guidance”

This is a good goal but currently underspecified.

Questions:

- What does “terse” mean in practice?
  - Avoid redundant nesting?
  - Avoid wide unions / `anyOf`?
  - Minimize optional fields?
- What does “optimized for guidance” mean?
  - Every field MUST have a clear `description` aimed at an AI/Human?
  - Use `examples`?
  - Use constrained types (enums, regexes) where possible to reduce search space?
- Do you expect to **customize Pydantic’s JSON Schema** (e.g., via `model_config` / `json_schema_extra`) to better match RDF/OWL semantics?

**Suggestion:**

- Add a few concrete guidelines, for example:
  - Each structural element field MUST have:
    - A descriptive `Field(..., description="...")` oriented toward both RDF/OWL meaning and agent usage.
    - Tight types (enums, constrained strings) where possible.
  - The generated schema for each structural element SHOULD be small enough to be comfortably embedded into middleware prompts (e.g., no huge recursive schemas).

That will give middleware authors something actionable.

#### 3.5. Error message shape and lifecycle

You say:

- “Structural elements MUST validate their fields and yield error messages that are guidance supporting correction of the error by an AI/Agent or Human.”

Open questions:

- **Where** do these errors surface?
  - Only via Pydantic validation exceptions?
  - Or also via domain-level checks (e.g., `.validate()` methods or specialized exceptions)?
- **Format**:
  - Free-form English text (current style)?
  - Should there be structured metadata (`code`, `hint`, `field`) so agents can systematically react?
- **Determinism and stability**:
  - For agents to rely on them, you’ll likely want error structures that don’t change arbitrarily.

Given your reliance on LangChain middleware ([docs](https://docs.langchain.com/oss/python/langchain/middleware/custom)), it might be valuable to define an _expected_ shape for errors that middleware hooks (e.g., `after_model`, `wrap_tool_call`) can interpret.

**Suggestion:**

- Decide whether:
  - It’s enough to rely on standard Pydantic error structures (which are already structured), and
  - You want to constrain the **error message text** portion to be instructional (“To fix this, do X”), not just descriptive.
- Consider stating something like:
  - “Validation errors MUST provide: (a) a stable error code, and (b) a natural-language hint describing how to correct the input.”

#### 3.6. Relationship to LangChain middleware state schemas

Motivator: “Structural elements are REQUIRED to support `rdflib-reasoning-middleware` implementations and best practices from LangChain middleware.”

Right now the proposal doesn’t say:

- Whether structural elements will be used as:
  - `AgentState` subclasses (custom state schema),
  - Tool argument/response models,
  - Or separate domain models that middleware maps into `AgentState`.

Given the LangChain patterns ([Custom middleware docs](https://docs.langchain.com/oss/python/langchain/middleware/custom)), it might be worth clarifying:

- “Structural elements are primarily domain models; middleware MAY map them into `AgentState` or tool schemas, but they do not themselves HAVE to inherit from `AgentState`.”
- Or, if you intend them to double as state, say so.

This will influence how tightly you couple the axioms package to LangChain types.

#### 3.7. Interaction with existing axioms package requirements

`rdflib-reasoning-axioms/AGENTS.md` already says:

- MUST support round-trip `graph -> axiomatization -> graph`.
- MUST follow `owl2-mapping-to-rdf` and transitive specs (`rdf11-semantics`).

Your proposal is compatible, but it would be useful to **explicitly connect**:

- That each `StructuralElement`:
  - Corresponds to a well-identified OWL 2 structural element in the spec.
  - Has `as_triples` that align with `owl2-mapping-to-rdf`.

This will help future readers see how the Pydantic hierarchy is grounded in the formal spec, not just invented for agents.

---

### Summary

1. **Principles:** Yes—agent-first Pydantic models, no embedded graphs, context-based scoping, spec-aligned structural modeling, and middleware-oriented schema/validation are all clear, coherent principles, though they’d benefit from being made explicit rather than implicit.

2. **Consistency:** The proposal is consistent with the root `README.md`, architecture docs, `AGENTS.md`, and the stated role of `rdflib-reasoning-middleware` as LangChain custom middleware. It largely formalizes patterns you’ve already started (Pydantic + RDFLib + agent research).

3. **Clarifications before a DR:** You should tighten:
   - The exact scope of “structural element” and required inheritance patterns.
   - The allowed vs. forbidden rdflib/third-party types inside models.
   - The semantics of `GraphBacked.context` and what “related” means.
   - Concrete criteria for “terse, guidance-optimized” JSON Schema.
   - The shape and lifecycle of validation errors for agents.
   - The mapping between structural elements and LangChain middleware state/tool schemas.
   - The explicit connection to OWL2 mapping specs.

If you’d like, the next step could be to turn these into explicit “Decision” and “Consequences” bullets you can later plug into the new DR, without actually drafting the DR text yet.

---

**User**

Please review the following to see if it clarifies those oversights / ambiguities, and if there is further refinement rhat would be reccomended.

3.1. Scope and Hierarchy of "structural elements"

- I primarily mean _any_ data model that may find itself at the interface of `rdflib-reasoning-middleware`. In general, we'd need to have a STRONG reason to deviate from this default and it would need to be well-documented. In general, preserving the restriction is is expected to expand the capabilities of an agent.
- As a non-OWL2 use case, we SHOULD consider `GraphBacked` elements that are triple-statements as found in RDF 1.2 (i.e., RDF-Star)
- `GraphBacked` is the proper universal base. It allows us to define axioms / patterns that are _not_ part of the OWL 2 Abstract Syntax and Structural Specification. That being said, `StructuralElement` MUST be the universal base for all things structural under OWL 2.

3.2. Boundary of complex third-party-data strutures

- Your suggestion is exactly  the correct inerpretation and it is what we should document.

3.3. semantics of `GraphBacked.context`

- Triples generated by `as_triples` could be converted to quads by adding `context` as a fourth element to each triple (and we should probably add a concrete `as_quads` method which codifies this).
- For simplicity, we'll only allow elements to have a single (required) context. This allows some functionality to arise trivially, e.g., equality for sets of elements.
- Cross-graph references occur as they would with RDF 1.1 dataset semantics; the graph that an entity is defined in is not part of the relationship. (NOTE: If this contradicts the `rdf11-datasets` specification's specified semantics, please inform me. Do not comment on conformance `rdf11-datasets` if I am not mistaken).

3.4. JSON Schema requirements

3.4.1. Let's examine "terse"

I imagine that it would be proper to define it as follows, but suggestions are welcome:

- Assumes that the documentation for the enclosing class, its other fields, and their data types are all present in the context (i.e., the "joint documentation").
- It SHOLD optimize context usage by complementing the joint documentation.
- It SHOULD NOT attempt to explain other fields except to capture its relationship with those fields. The complete interaction MUST emerge from looking at the joint documentation. Complex interaction SHOULD be documented at the level of the enclosing class.
- It MUST NOT assume that module documentation or any repository content is part of the "joint documentation". It is REQUIRED to only assume documentation that would become part of pydantic's generated JSON schema.
- It MUST NOT use examples except when instructed to by the user; this will typically only happen to correct a pattern of repeated misuse.
- It SHOULD refer to the governing specification where they apply (e.g., `A IETF BCP 47 language tag`).

3.4.2. Optimized for guidance

- It SHOULD use constrained types whereever possible; it MUST NOT use constrained types without approval from a user.
- Errors MUST explicitly specify illegal values to reduce the cognitive load  that debuggig places on an agent/human.
- Errors SHOULD explicity define valid ranges (e.g., `a nonzero positive integer`, `a RFC 3987 IRI`, `one of {'a', 'b'}`). Valid ranges may be omitted if they would _increase_ cognitive load (e.g., a regex pattern for valid RFC 3987 IRIs).
- Errors SHOULD reccomend a fix (e.g., `validate the derivation of the value and try again`, `you should use function_y, instead`
- If an error represents the violation of a specification constraint, then the error MUST indicate the specification & section as a reference.

3.5. Error message shape and lifecycle

- All checks, though domain-level checks SHOULD be performed as a consequence of pydantic validation
- Free-form english text - Developers SHOULD strive for consistency but MAY deviate when exceptions are exceptional.
- Current error shapes are not constrained, and we should tackle them in a future decision.

3.6. Relationship to LangChain middleware

- Structural elements MUST be able to be used as tool argument/response models
- CRITICAL: `GraphBacked` elements MUST be stateless and immutable
- `GraphBacked` elements MUST NOT be `AgentState` subclasses

3.7. Interaction with existing axiom package requirements

- I believe that I indicate that concrete `StruturalElement` subclasses must correspond to well-identified elements in some class documentation, correct?
- I agree that we should capture that in this decision.

---

**Cursor**

### Overall

These clarifications go a long way toward resolving the earlier ambiguities. They mostly strengthen the design and are consistent with your existing docs and with how `rdflib_reasoning.axiom.structural_element` is already shaping up. Below I’ll call out where they’re solid and where I’d still refine wording or loosen/tighten some constraints.

---

### 3.1 Scope and hierarchy of “structural elements”

- **Strength:** The split between “anything at the middleware interface” and “OWL 2 structural elements” is now clearer: `GraphBacked` = universal base for graph-scoped things; `StructuralElement` = universal base for OWL 2 structural elements.
- **Potential refinement:**
  - “Any data model that may find itself at the interface of middleware” is very broad. I’d narrow this to something like: **“Any domain data model that is intended to be passed across the middleware boundary (agent ↔ library) MUST be a Pydantic model, and MUST inherit from `GraphBacked` if it is graph-scoped.”**
  - Explicitly say: **“Every OWL 2 structural element represented in this package MUST subclass `StructuralElement`, which itself inherits from `GraphBacked`.”**
  - Calling out RDF-star-style triple-statements as **`GraphBacked` but not necessarily `StructuralElement`** is good; I’d make that explicit as a motivating example.

---

### 3.2 Boundary of complex third‑party data structures

- Your adoption of the earlier interpretation (allow rdflib node/identifier types, forbid container-like objects such as `Graph` or query results) is solid.
- I’d just phrase it explicitly as a rule in the DR: **“Structural elements MAY contain rdflib node-level types (`URIRef`, `BNode`, `Literal`, `IdentifiedNode`, etc.) but MUST NOT contain `rdflib.Graph`, `ConjunctiveGraph`, SPARQL result objects, or other container/session/handle types.”**

---

### 3.3 Semantics of `GraphBacked.context`

- **Single required context** and **“quads = triples + context”** are clear and implementation-friendly; an `as_quads()` helper is a good concrete consequence.
- The statement about cross-graph references matches RDF 1.1 datasets semantics: the graph name is metadata about where a triple appears, not part of the triple’s predicate/object. So “the graph that an entity is defined in is not part of the relationship” is consistent, provided you’re talking about the RDF semantics, not some application-specific closed-world constraint.
- I’d still recommend:
  - Defining “related” in terms of **structural references**: e.g., “If a `GraphBacked` instance has a field whose type is another `GraphBacked` (or `StructuralElement`) instance, those two MUST share the same `context`.”
  - Clarifying that **cross-context relationships are expressed only at the triple/quad level**, not by embedding foreign-context `GraphBacked` instances.

---

### 3.4 JSON Schema requirements

#### 3.4.1 “Terse”

- The idea of **“joint documentation = exactly what appears in the Pydantic-generated schema”** is good: it gives you a bounded context.
- The rules about:
  - Complementing rather than duplicating other field/class docs,
  - Avoiding non-schema docs as assumptions,
  - Moving complex interaction docs to the enclosing class,
  - Referring to governing specs (e.g. RFCs),

  are all sound and aligned with “agent-guidable” schemas.

- Two potential tensions / refinements:
  - **“MUST NOT use examples except when instructed by the user”** is very strict.
    - In practice, JSON Schema examples are often extremely helpful for LLM guidance. You might prefer: “Examples SHOULD be used sparingly and only when they significantly reduce misuse; they MUST NOT be verbose or redundant.”
  - The constraint “It MUST NOT assume module documentation or any repository content” is consistent, but you might want to **allow referring to specs or DRs by identifier** (e.g., “See OWL2 Mapping to RDF §X.Y” or a DR ID) because those references can still be in schema descriptions.

#### 3.4.2 “Optimized for guidance”

- Good:
  - Constrained types **SHOULD** be used where they sharply reduce the search space.
  - Errors specifying illegal values, valid ranges, and recommended fixes is exactly what agents need.
  - Spec+section references in spec-violation errors is excellent.
- I see one tension to resolve:
  - “It SHOULD use constrained types wherever possible; it MUST NOT use constrained types without approval from a user.”
    - That effectively makes constrained types opt-in only. Given the goal of an **agent-first library**, I’d instead codify some **library-level defaults** (e.g., constrained IRIs, language tags) and say:
      - “Constrained types MAY be introduced by library authors when they reflect normative spec constraints or clear domain invariants; users MAY loosen them by agreement if the use case demands it.”
- Also, for ranges and formats where regexes are too heavy (IRIs, language tags), I like your suggestion to keep them out of error messages to avoid cognitive overload.

---

### 3.5 Error message shape and lifecycle

- Aligning domain checks with Pydantic validation is good; it keeps one unified validation surface.
- Relying on **free-form English** only is acceptable for now, but it’s worth explicitly marking as **“status quo, subject to future decision.”** You already say current shapes are not constrained and will be tackled in a future DR; that’s the right posture.
- If you want to future‑proof this, you might add a weak requirement:
  - “Where feasible, errors SHOULD follow a consistent pattern of: short summary, illegal value(s), valid range hint, and (if applicable) specification reference.”
  That keeps them human/LLM friendly without locking you into a rigid error schema yet.

---

### 3.6 Relationship to LangChain middleware

- The three bullets draw a very clear boundary:
  - **Tool argument/response models:** Structural/`GraphBacked` elements MUST be usable in these roles → strongly compatible with LangChain’s Pydantic-based tooling.
  - **Stateless and immutable:** Critical for deterministic behavior and safe use as state snapshots or tool arguments.
  - **MUST NOT be `AgentState` subclasses:** This cleanly decouples domain models from LangChain’s state machinery.

- I’d add one clarifying sentence (even if just in commentary in the DR):
  - “Middleware MAY map `GraphBacked` / `StructuralElement` instances into `AgentState` fields, but the domain types themselves remain independent of LangGraph’s state base classes.”
- And, if you want to be explicit about how these are used:
  - Note that they are intended as:
    - Tool inputs/outputs, and
    - Payloads carried inside `AgentState` (e.g. `current_axioms: list[StructuralElement]`), not `AgentState` themselves.

---

### 3.7 Interaction with existing axioms package requirements

- Yes, your current `StructuralElement` docstring hints at a link to OWL 2 structural specification (“An Element of the OWL 2 Structural Specification…”).
- I’d still make the mapping rule explicit in the DR:
  - “Every concrete `StructuralElement` subclass MUST correspond to a well-identified OWL 2 structural element (or clearly documented extension), and its `as_triples` MUST conform to the `owl2-mapping-to-rdf` specification (and its transitive dependencies such as `rdf11-semantics`).”
- For non-OWL constructs (e.g. RDF-star triple-statements as `GraphBacked`), I’d mention that they:
  - Either map to RDF 1.2/RDF-star drafts/specs, or
  - Are clearly documented as extensions with their own references.

---

### Closing

In summary, your additions substantially clarify the earlier ambiguities. The main refinements I’d consider are: narrowing the notion of “interface” models, slightly softening the bans on examples and constrained types while still favoring minimality, tightening the definition of “related” for `context`, and explicitly tying each `StructuralElement` to an OWL 2 element + `owl2-mapping-to-rdf` mapping. Everything else looks well-aligned with the repo’s goals and with LangChain middleware best practices.

---

**User**

We shold apply your reccomendations, update existing documentation in the code, introduce `as_quads`, and create a  /new-decision-record . There are a few addition clarifications I'd like to make:

3.4.1. Terse

- I agree with your reccomendation for sparing usage of examples
- We MAY reference identifiers for specifications, but we MUST NOT reference decision records / etc. The **Runtime**/deployed agent is a _different_ agent than the **Code Assistant** that maintains the system. Decision records are meaningless to the deployed agent and they do not have access to them. Specifications references MUST use official identifiers, and not our repository-local ones, nor may they reference specific content from `optimized.html` / etc.

3.4.2. "Optimized for guidance"

- I mistyped, "It SHOULD use constrained types wherever possible; it MUST NOT use **UN**constrained types without approval from a user.” I strongly prefer to the usage of constrained type to reduce cognitive load and provide assistance to agents/developers.

3.5. Error messages - Let's future proof it per your reccomendation.

Implement the plan as specified, it is attached for your reference. Do NOT edit the plan file itself.

To-do's from the plan have already been created. Do not create them again. Mark them as in_progress as you work, starting with the first one. Don't stop until you have completed all the to-dos.

---

**Cursor**

Implementing the plan step by step. Gathering the necessary files and starting the first todo.

Implementing structural_element changes: updating docstrings and adding `as_quads`.

Adding a validator on `Seq` to ensure all elements share the same `context`:

Adding a brief pointer in the root AGENTS.md:

Checking the table: we have `rdflib-reasoning-agents` and `rdflib-reasoning-middleware` as separate packages.

Adding a table row for `rdflib-reasoning-middleware` and shortening the agents row.

Creating the new decision record and updating the index.

Adding a brief reference in the architecture doc per the decision-records AGENTS.md:

Summary of what was implemented:

**1. Structural element core ([rdflib-reasoning-axioms/src/rdflib_reasoning/axiom/structural_element.py](rdflib-reasoning-axioms/src/rdflib_reasoning/axiom/structural_element.py))**

- **GraphBacked:** Docstring updated to describe it as the base for graph-scoped Pydantic models; single required `context`; no embedding of `rdflib.Graph` or other heavy types; allowed use of rdflib node types; related elements share the same context; cross-context only at triple/quad level. Fixed typo “MUST bedefined” → “MUST be defined”.
- **StructuralElement:** Docstring updated to state it is the base for OWL 2 structural elements, with concrete subclasses corresponding to well-identified OWL 2 elements and `as_triples`/`as_quads` conforming to the specs. Added concrete **`as_quads`** returning `Sequence[Quad]` by appending `self.context` to each triple from `as_triples`. Import of `Quad` from `common` added.
- **Seq:** Validator added so every element in `elements` shares the same `context` as the `Seq`; violation raises a clear `ValueError`.

**2. Type boundaries and context (axioms AGENTS.md)**

- New section **“Structural elements and GraphBacked”**: GraphBacked vs StructuralElement bases; concrete StructuralElement ↔ OWL 2 element and spec conformance; RDF-star as GraphBacked-only; allowed rdflib node types; no Graph/ConjunctiveGraph/SPARQL results; single required `context`; related elements same context and validators; cross-context only at triple/quad level.

**3. JSON Schema and error conventions (axioms AGENTS.md + root AGENTS.md)**

- **“JSON Schema: terse and optimized for guidance”**: Joint documentation = Pydantic JSON Schema only; no assumption of module/repo/DRs/internal artifacts; MAY reference official spec identifiers (no DR or repo-local refs); descriptions complement joint docs; examples sparing; constrained types preferred, unconstrained only with explicit approval.
- **“Validation errors”**: Domain checks via Pydantic; errors specify illegal values and valid ranges; recommend a fix; spec violations cite spec + section; consistent pattern (summary, illegal values, range hint, spec ref) with room for a future DR to fix exact shape.

**4. LangChain middleware (middleware README + root AGENTS.md)**

- **rdflib-reasoning-middleware/README.md:** GraphBacked/StructuralElement usable as tool args and responses and as state payloads; stateless and immutable; MUST NOT subclass `AgentState`; middleware MAY map them into `AgentState` fields.
- **Root AGENTS.md:** New table row for `rdflib-reasoning-middleware/` with link to its README; axioms row points to its AGENTS.md for GraphBacked/StructuralElement and schema/error rules.

**5. New decision record**

- **Created** [docs/dev/decision-records/DR-002 Structural Elements and Middleware Integration.md](docs/dev/decision-records/DR-002%20Structural%20Elements%20and%20Middleware%20Integration.md) (Status: Accepted) with Context, Decision (Pydantic hierarchy, no embedded graphs, context/as_quads, OWL 2 alignment, JSON Schema rules, validation errors, LangChain middleware), Consequences, and no Supersedes.
- **Updated** [docs/dev/decision-records/INDEX.md](docs/dev/decision-records/INDEX.md) with a row for 2025-03-09 linking to DR-002.
- **Updated** [docs/dev/architecture.md](docs/dev/architecture.md) with a sentence that structural elements and middleware integration are governed by DR-002 and point to the DR.
