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format is an annotation by default (option 2) #1026

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7e09ca0
resolves #1020 - format is an annotation by default
gregsdennis Nov 20, 2020
b0b6777
removed a redundancy
gregsdennis Nov 20, 2020
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91 changes: 31 additions & 60 deletions jsonschema-validation.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -566,90 +566,61 @@
<cref>This is due to the keyword's history, and is not in line with current
keyword design principles.</cref> In order to manage this ambiguity, the
"format" keyword is defined in its own separate vocabulary, as noted above.
The true or false value of the vocabulary declaration governs the implementation
requirements necessary to process a schema that uses "format", and the
behaviors on which schema authors can rely.
</t>
<t>
Regardless of the boolean value of the vocabulary declaration,
an implementation that can evaluate "format" as an assertion MUST provide
options to enable and disable such evaluation. The default behavior MUST be
to collect annotations.
</t>

<section title="As an annotation">
<t>
The value of format MUST be collected as an annotation, if the implementation
supports annotation collection. This enables application-level validation when
schema validation is unavailable or inadequate.
</t>
<t>
This requirement is not affected by the boolean value of the vocabulary
declaration, nor by the configuration of "format"'s assertion
behavior described in the next section.
<cref>
Requiring annotation collection even when the vocabulary is declared with
a value of false is atypical, but necessary to ensure that the best
practice of performing application-level validation is possible even when
assertion evaluation is not implemented. Since "format" has always been
a part of this specification, requiring implementations to be aware of it
even with a false vocabulary declaration is deemed to not be a burden.
This requirement is not affected by the boolean value of the vocabulary
declaration.
For a vocabulary value of true, the implementation MUST halt if it doesn't
understand the vocabulary. If the implementation does understand the
vocabulary, annotations are collected. This halt-on-non-understanding
behavior may be desired by an application, so it is considered. However,
this is the result of the behavior of the "$vocabulary" keyword exclusively
and is not affected by the definition of "format".
For a vocabulary value of false, the implementation MAY proceed without
understanding the keyword, meaning that the implementation will collect
its value as an annotation anyway.
</cref>
</t>
</section>

<section title="As an assertion">
<t>
Regardless of the boolean value of the vocabulary declaration,
an implementation that can evaluate "format" as an assertion MUST provide
options to enable and disable such evaluation. The assertion evaluation
behavior when the option is not explicitly specified depends on
the vocabulary declaration's boolean value.
When configured to process "format" as an assertion, an implementation MUST
implement syntactic validation for all format attributes defined
in this specification, and for any additional format attributes that
it recognizes, such that there exist possible instance values
of the correct type that will fail validation.
</t>

<t>
When implementing this entire specification, this vocabulary MUST
be supported with a value of false (but see details below),
and MAY be supported with a value of true.
</t>

<t>
When the vocabulary is declared with a value of false, an implementation:
<list>
<t>
MUST NOT evaluate "format" as an assertion unless it is explicitly
configured to do so;
</t>
<t>
SHOULD provide an implementation-specific best effort validation
for each format attribute defined below;
</t>
<t>
MAY choose to implement validation of any or all format attributes
as a no-op by always producing a validation result of true;
</t>
<t>
SHOULD document its level of support for validation.
</t>
</list>
It is understood that, due to computing limitations and other concerns,
it is improbable that an implementation will be able to perfectly cover
all of the requirements set forth by these formats. As such, it is
strongly RECOMMENDED for implementations to document their level of
support for validation.
<cref>
This matches the current reality of implementations, which provide
widely varying levels of validation, including no validation at all,
for some or all format attributes. It is also designed to encourage
relying only on the annotation behavior and performing semantic
validation in the application, which is the recommended best practice.
Furthermore, the more support an implementation has, the more users
it is likely to attract. This should encourage implementors to
provide the most comprehensive support they can.
</cref>
</t>

<t>
When the vocabulary is declared with a value of true, an implementation
that supports this form of the vocabulary:
<list>
<t>
MUST evaluate "format" as an assertion unless it is explicitly
configured not to do so;
</t>
<t>
MUST implement syntactic validation for all format attributes defined
in this specification, and for any additional format attributes that
it recognizes, such that there exist possible instance values
of the correct type that will fail validation.
</t>
</list>
The requirement for minimal validation of format attributes is intentionally
vague and permissive, due to the complexity involved in many of the attributes.
Note in particular that the requirement is limited to syntactic checking; it is
Expand All @@ -676,7 +647,7 @@
The <xref target="meta-schema">standard core and validation meta-schema</xref>
includes this vocabulary in its "$vocabulary" keyword with a value of false,
since by default implementations are not required to support this keyword
as an assertion. Supporting the format vocabulary with a value of true is
as an assertion. Supporting the format vocabulary as an assertion is
understood to greatly increase code size and in some cases execution time,
and will not be appropriate for all implementations.
</t>
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