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Fixes inconsistency in the definition versus the use of the 'Filter' algebra operator #255

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Fixes inconsistency in the definition versus the use of the 'Filter' algebra operator #255

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28 changes: 19 additions & 9 deletions spec/index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -9904,14 +9904,20 @@ <h3>SPARQL Algebra</h3>
described above.</p>
<div class="defn">
<p><b>Definition: <span id="defn_algFilter">Filter</span></b></p>
<p>Let <var>Ω</var> be a multiset of solution mappings and <var>expr</var> be an expression. We define:</p>
<p><a href="#defn_algFilter" class="algFct">Filter</a>(<var>expr</var>, <var>Ω</var>) = { <var>μ</var> | <var>μ</var> in <var>Ω</var> and <var>expr</var>(<var>μ</var>) is an expression that has an
<p>Let <var>Ω</var> be a multiset of solution mappings,
<var>expr</var> be an <a href="#expressions">expression</a>,
|D| be a <a href="#sparqlDataset">dataset</a>,
and |G| be the <a href="#defn_ActiveGraph">active graph</a>.
We define:</p>
<p><a href="#defn_algFilter" class="algFct">Filter</a>(<var>expr</var>, <var>Ω</var>, |D|, |G|) = { <var>μ</var> in <var>Ω</var> | <var>expr</var>(<var>μ</var>) is an expression that has an
effective boolean value of true }</p>
<p><a href="#defn_Multiplicity">multiplicity</a>( <var>μ</var> | <a href="#defn_algFilter" class="algFct">Filter</a>(<var>expr</var>, <var>Ω</var>) )
<div class="issue" data-number="254">
It is not clear what <var>expr</var>(<var>μ</var>) is, and it is not apparent in the formula that the expression |expr| is meant to be evaluated not only with respect to <var>μ</var> but also with respect to |D| with active graph |G|.</div>
<p><a href="#defn_Multiplicity">multiplicity</a>( <var>μ</var> | <a href="#defn_algFilter" class="algFct">Filter</a>(<var>expr</var>, <var>Ω</var>, |D|, |G|) )
= <a href="#defn_Multiplicity">multiplicity</a>( <var>μ</var> | <var>Ω</var> )</p>
Comment on lines +9911 to 9917
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It appears likely that these <p> should instead be a list (I think unordered, but I could be wrong) beneath the We define: which I suggest should be changed to We define the following:

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Any other instances of We define:</p> and subsequent <p> should get similar handling.

I agree with the We define the following:.

Your other suggestion (to present each block of formulas as a list) is a matter of taste, I guess.

In any case, these changes are not related to the purpose of this PR and, thus, I would keep them for a separate PR (to be created after this one is merged). I created an issue to remember this TODO: #258

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I'm not convinced by the " the following" which to me suggests "one or more".

It's not separate items - it's a unit (singular).

<blockquote>
Note that evaluating an <code>exists(pattern)</code> expression uses the dataset and
active graph, D(G). See the <a href="#defn_evalFilter">evaluation of filter</a>.
Note that evaluating an <code>exists(pattern)</code> expression uses the dataset |D| and
active graph |G|. See the <a href="#defn_evalFilter">evaluation of filter</a>.
</blockquote>
</div>
<div class="defn">
Expand All @@ -9933,10 +9939,12 @@ <h3>SPARQL Algebra</h3>
<div class="defn">
<p><b>Definition: <span id="defn_algDiff">Diff</span></b></p>
<p>Let <var>Ω<sub>1</sub></var> and <var>Ω<sub>2</sub></var> be multisets of solution mappings and <var>expr</var> be an
expression. We define:</p>
<a href="#expressions">expression</a>. We define:</p>
<p><a href="#defn_algDiff" class="algFct">Diff</a>(<var>Ω<sub>1</sub></var>, <var>Ω<sub>2</sub></var>, <var>expr</var>) = { <var>μ</var> | <var>μ</var> in <var>Ω<sub>1</sub></var> such that ∀ <var>μ'</var> in
<var>Ω<sub>2</sub></var>, either <var>μ</var> and <var>μ'</var> are not <a href="#defn_algCompatibleMapping">compatible</a> or <var>μ</var> and <var>μ'</var> are <a href="#defn_algCompatibleMapping">compatible</a> and
<var>expr</var>(merge(<var>μ</var>, <var>μ'</var>)) does not have an effective boolean value of true }</p>
<div class="issue" data-number="254">
It is not clear what <var>expr</var>(<var>μ</var>) is, and it is not apparent in the formula that the expression |expr| is meant to be evaluated not only with respect to <var>μ</var> but also with respect to |D| with active graph |G|.</div>
<p><a href="#defn_Multiplicity">multiplicity</a>( <var>μ</var> | <a href="#defn_algDiff" class="algFct">Diff</a>(<var>Ω<sub>1</sub></var>, <var>Ω<sub>2</sub></var>, <var>expr</var>) ) =
<a href="#defn_Multiplicity">multiplicity</a>( <var>μ</var> | <var>Ω<sub>1</sub></var> )</p>
Comment on lines +9942 to 9949
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As with above We define: and subsequent <p>.

</div>
Expand All @@ -9946,7 +9954,7 @@ <h3>SPARQL Algebra</h3>
<div class="defn">
<p><b>Definition: <span id="defn_algLeftJoin">LeftJoin</span></b></p>
<p>Let <var>Ω<sub>1</sub></var> and <var>Ω<sub>2</sub></var> be multisets of solution mappings and <var>expr</var> be an
expression. We define:</p>
<a href="#expressions">expression</a>. We define:</p>
<p><a href="#defn_algLeftJoin" class="algFct">LeftJoin</a>(<var>Ω<sub>1</sub></var>, <var>Ω<sub>2</sub></var>, <var>expr</var>) = <a href="#defn_algFilter" class="algFct">Filter</a>(<var>expr</var>, <a href="#defn_algJoin" class="algFct">Join</a>(<var>Ω<sub>1</sub></var>,
<var>Ω<sub>2</sub></var>)) ∪ <a href="#defn_algDiff" class="algFct">Diff</a>(<var>Ω<sub>1</sub></var>, <var>Ω<sub>2</sub></var>, <var>expr</var>)</p>
<p><a href="#defn_Multiplicity">multiplicity</a>( <var>μ</var> | <a href="#defn_algLeftJoin" class="algFct">LeftJoin</a>(<var>Ω<sub>1</sub></var>, <var>Ω<sub>2</sub></var>, <var>expr</var>) ) =
Comment on lines +9957 to 9960
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As with above, and extending down to line 9963.

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Any other instances of We define:</p> and subsequent <p> should get similar handling.

Expand Down Expand Up @@ -9984,6 +9992,8 @@ <h3>SPARQL Algebra</h3>
<p>Let <var>μ</var> be a solution mapping, <var>Ω</var> a multiset of solution mappings, <var>var</var> a variable
and <var>expr</var> be an <a href="#expressions">expression</a>, then we define:</p>
<p><a href="#defn_algExtend" class="algFct">Extend</a>(<var>μ</var>, <var>var</var>, <var>expr</var>) = <var>μ</var> ∪ { (<var>var</var>, <var>value</var>) | <var>var</var> not in dom(<var>μ</var>) and <var>value</var> = <var>expr</var>(<var>μ</var>) }</p>
<div class="issue" data-number="254">
It is not clear what <var>expr</var>(<var>μ</var>) is, and it is not apparent in the formula that the expression |expr| is meant to be evaluated not only with respect to <var>μ</var> but also with respect to |D| with active graph |G|.</div>
<p><a href="#defn_algExtend" class="algFct">Extend</a>(<var>μ</var>, <var>var</var>, <var>expr</var>) = <var>μ</var> if <var>var</var> not in dom(<var>μ</var>) and expr(<var>μ</var>) is an error</p>
<p><a href="#defn_algExtend" class="algFct">Extend</a> is undefined if <var>var</var> in dom(<var>μ</var>).</p>
<p><a href="#defn_algExtend" class="algFct">Extend</a>(<var>Ω</var>, <var>var</var>, <var>expr</var>) = { <a href="#defn_algExtend" class="algFct">Extend</a>(<var>μ</var>, <var>var</var>, <var>expr</var>) | <var>μ</var> in <var>Ω</var> }</p>
Expand Down Expand Up @@ -10437,7 +10447,7 @@ <h3>Evaluation Semantics</h3>
<ul>
<li>|P|, <var>P<sub>1</sub></var>, <var>P<sub>2</sub></var> : graph patterns</li>
<li>|L| : a solution sequence</li>
<li>|F| : an expression</li>
<li>|F| : an <a href="#expressions">expression</a></li>
</ul>
<div class="issue" data-number="225">
The definitions in this section do not cover the cases in which
Expand All @@ -10454,7 +10464,7 @@ <h3>Evaluation Semantics</h3>
</div>
<div class="defn">
<p><b>Definition: <span id="defn_evalFilter">Evaluation of Filter</span></b></p>
<p><a href="#defn_eval" class="evalFct">eval</a>( |D|(|G|), <a href="#defn_absFilter" class="absOp">Filter</a>(|F|, |P|) ) = <a href="#defn_algFilter" class="algFct">Filter</a>( |F|, <a href="#defn_eval" class="evalFct">eval</a>(|D|(|G|), |P|), |D|(|G|) )</p>
<p><a href="#defn_eval" class="evalFct">eval</a>( |D|(|G|), <a href="#defn_absFilter" class="absOp">Filter</a>(|F|, |P|) ) = <a href="#defn_algFilter" class="algFct">Filter</a>( |F|, <a href="#defn_eval" class="evalFct">eval</a>(|D|(|G|), |P|), |D|, |G| )</p>
</div>
<p>'substitute' is a filter function in support of the evaluation of
<a href="#func-filter-exists"><code>EXISTS</code>
Expand Down
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