Explain JSON-LD further.

index.html

@@ -3950,42 +3950,176 @@ <h2>Syntaxes</h2>
       <section>
         <h3>JSON-LD</h3>
 
-        <p>
+        <section class="informative">
+          <h4>Data Model Foundations</h4>
+          <p>
+  The world of credentials is vast and varied. A physical wallet places a few
+  constraints on the shape and size of those credentials, and no restriction on
+  their contents. Likewise, the Verifiable Credential Data Model's use of
+  [[!JSON-LD]] provides a consistent way to interpret all compliant Verifiable
+  Credentials using a syntax that can be enforced using complementary
+  technologies such as JSON Schema. This means issuers can add claim terminology
+  unique to their communities without the high costs of centralized terminology
+  registration or format churn. In turn, digital wallets can store and index
+  credentials with widely varying content, providing value to a plethora of
+  communities, and enabling many diverse use cases.
+          </p>
+          <p>
+  [[!JSON-LD]] provides the Verifiable Credential Data Model (VCDM) with
+  consistent object-oriented modeling constraints that are familiar to
+  developers and enable better reuse and composition of data. That modeling is
+  built from clean expressions of <em>subjects, properties, and values</em>
+  (<em>S-P-V</em>, also referred to as <em>entities, attributes, and values</em>,
+  <em>E-A-V</em>, as well as <em>subjects, predicates, and objects</em>,
+  <em>S-P-O</em>) which comprise the shape of each atomic claim within a VCDM
+  credential. This approach empowers Wallets to store any credential shaped in
+  this way and to index the contained claims across all the holder's
+  credentials, such that credentials may be quickly and easily found and
+  presented when needed.
+          </p>
+
+          <p>
+  This foundational data modeling and grammatical structure is provided through
+  the addition of a single `@context` key which identifies context files that map
+  otherwise idiosyncratic and often ephemeral terms into universally shareable,
+  collision resistant vocabularies. [[!JSON-LD]] provides the VCDM's
+  underlying subject, property, and value graph-based data model which enables
+  aggregation, collation, and even separation of the individual statements held
+  within the [[!JSON-LD]] graph. It expresses this model using a developer-friendly
+  object-oriented structure enabling consistent interpretation of previously
+  freeform JSON documents.
+          </p>
+        </section>
+
+        <section class="informative">
+          <h3>Extending JSON</h3>
+
+          <p>
+[[!JSON-LD]] brings context, meaning, and object-oriented modeling to previously
+idiosyncratic JSON formats. It provides that contextualization by mapping
+colloquial terms used within a JSON object to term and type definitions with
+universal identifiers in the form of URLs. This prevents  term collisions and
+need for yet-more-JSON-formats by providing a common extensible JSON structure
+with minimal requirements for extensibility. The additional grammatical
+constraints at this foundational layer prevent the need for endless invention
+and support of use case specific JSON models with idiosyncratic terms and
+unique to the implementation approaches to data modeling, value usage, and
+parsing approaches.
+          </p>
+
+          <p>
+A JSON document becomes a [[!JSON-LD]] document when it includes an `@context`
+property with a URL associated with a context file and is interpreted in an
+object-oriented style. The context file provides
+the mapping between the idiosyncratic in-document terminology and universally
+shareable identifiers and value definitions. This provides not only
+contextualization and meaning, but also reusability through universally
+shareable terms and object-oriented structuring. This enables aggregation and
+collation of data without the need for additional upfront integration
+development time for each newly discovered JSON format. Future community
+credential definitions will focus on the use of their terminology rather than
+force implementers to parse another unique JSON format specific to that
+community or use case.
+          </p>
+
+          <p>
+Consequently, without any additional processing a JSON document gains the value
+of an in-message association with its terminology definitions. Details on
+processing VCDM documents consistently with the context file, but without
+[[!JSON-LD]] tooling, can be found in the "JSON Processing" section below.
+          </p>
+
+          <p>
+The referenced context file provides the foundation for a consistent
+grammatical layer on top of object-oriented modeling and community-driven
+terminology selection which enables coexistence of various JSON tree shapes and
+colloquial terms while preventing likely terminology collisions or creating a
+need to write new tree traversal code for every new media type or JSON shape or
+parsing approach.
+          </p>
+
+          <p>
+The Verifiable Credentials Data Model uses this consistent foundation to provide a
+common layer across all credentials, presentations, and transaction formats
+within a single, consistently parseable media type definition. This allows for
+ecosystem extensibility without requiring a centralized registry to be updated
+for every new application or community. The core data model terms are
+registered and specified while communities are free to build on that foundation
+through their own specification process. The terminology mappings are
+referenced from the VCDM document removing the need for an ever changing
+landscape of "private claims" or narrowly defined "public claims" housed in a
+centralized registry. Instead, contexts function as decentralized registries
+that can be shared within or across communities. The common grammar and
+object-oriented data modeling
+remain the same, and properly contextualized terms can commingle. Applications
+and communities can extend what is claimed and signed through the use of
+vocabularies.
+          </p>
+
+          <p>
+The underlying graph data model enables signing of the document's statements
+rather than just an envelope in which it's contained. When using this feature, the
+data — while signed — is accessible in the same format it had been prior to signing,
+allowing for easier indexing, storage, and in-Wallet selection. The existence of
+one or more proofs within the object-oriented graph model, each fit for purpose,
+can be used to increase confidence that its actual informational contents are signed.
+This enables, for example, selective disclosure of statements within the same JSON format,
+avoiding the ever increasing cost of retooling for new disclosure formats or
+new envelope types. The proof is consistently placed alongside the claims.
+          </p>
+
+          <p>
+[[!JSON-LD]] provides Verifiable Credentials with a consistent grammatical
+foundation, object-oriented modeling, and collision-free terminology sharing
+which allows for ecosystem growth, document format iteration (rather than
+reinvention), and an extensible framework for new cryptographic proof
+mechanisms without altering or damaging the underlying data structure. This
+creates economies of scale which reduces development time, decreases
+retooling cost, decreases time to market, and provides long term stability for
+Issuers, Verifiers, and Wallets.
+          </p>
+        </section>
+
+        <section>
+          <h3>JSON-LD Syntax</h3>
+
+          <p>
 [[!JSON-LD]] is a JSON-based format used to serialize
 <a href="https://www.w3.org/TR/ld-glossary/#linked-data">Linked Data</a>. The
 syntax is designed to easily integrate into deployed systems already using JSON,
 and provides a smooth upgrade path from JSON to [[!JSON-LD]]. It is primarily
 intended to be a way to use Linked Data in Web-based programming environments,
 to build interoperable Web services, and to store Linked Data in JSON-based
 storage engines.
-        </p>
+          </p>
 
-        <p>
+          <p>
 [[!JSON-LD]] is useful when extending the data model described in this
 specification. Instances of the data model are encoded in JSON-LD compact
 form [[!JSON-LD]] and include the <code>@context</code> <a>property</a>. The
 <a href="https://www.w3.org/TR/json-ld/#the-context">JSON-LD context</a>
 is described in detail in the [[!JSON-LD]] specification and its use is
 elaborated on in Section <a href="#extensibility"></a>.
-        </p>
+          </p>
 
-        <p>
+          <p>
 Multiple contexts MAY be used or combined to express any arbitrary information
 about <a>verifiable credentials</a> in idiomatic JSON. The
 <a href="https://www.w3.org/TR/json-ld/#the-context">JSON-LD context</a>,
 available at <code>https://www.w3.org/ns/credentials/v2</code>, is a static
 document that is never updated and can therefore be downloaded and cached client
 side. The associated vocabulary document for the Verifiable Credentials Data
 Model is available at <code>https://www.w3.org/2018/credentials</code>.
-        </p>
+          </p>
 
-        <p>
+          <p>
 This specification restricts the usage of JSON-LD representations of
 the data model. JSON-LD <a
 href="https://www.w3.org/TR/json-ld/#compacted-document-form">compact document
 form</a> MUST be utilized for all representations of the data model in the
 base media type, `application/vc+ld+json`.
-        </p>
+          </p>
+        </section>
 
         <section>
           <h3>Syntactic Sugar</h3>