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<div class="section" id="selectors-for-data-package-components">
<h1>Selectors for Data Package Components<a class="headerlink" href="#selectors-for-data-package-components" title="Permalink to this headline">¶</a></h1>
<div class="section" id="goal">
<h2>Goal<a class="headerlink" href="#goal" title="Permalink to this headline">¶</a></h2>
<p>Develop a generalized selector API and standard that can be used to
identify granules within a data resource (data set, data package, composite
object) that is managed by DataONE. The “selector†can be appended to an
identifier or included with an API call to retrieve an object and the response
is the sub-element or component specified by the selector.</p>
<p>Types of selector are likely to vary with the types of composite objects being
managed by DataONE. For example, a selector may be defined to return a range
by bytes from a BLOB, or perhaps a single file from within a zip archive of a
set of files.</p>
<p>Some examples:</p>
<ul class="simple">
<li>Byte range (first and last offset, or first offset and size)</li>
<li>Index range (offset into a list)</li>
<li>HTML fragment identifier</li>
<li>Time offset or range</li>
<li>Bounding box spatial range</li>
<li>Database record selection from a key</li>
</ul>
</div>
<div class="section" id="rationale">
<h2>Rationale<a class="headerlink" href="#rationale" title="Permalink to this headline">¶</a></h2>
<p>There are practical limits to the total number of objects that may
be effectively managed at the level of detail supported by the DataONE
infrastructure. By managing content at the collection or package level, the
total number of managed identifiers can be constrained to a more manageable
range (e.g. a single collection may have >= 1e5 elements or records). Using
selectors, this could be reduced to a single identifier for the collection
plus support for the appropriate selector.</p>
<p>So a “selector service” is implemented by a node as a mechanism for retrieving
some object that exists as a sub-component of a larger object that is managed
by the DataONE infrastructure.</p>
</div>
<div class="section" id="implications-for-implementation">
<h2>Implications for Implementation<a class="headerlink" href="#implications-for-implementation" title="Permalink to this headline">¶</a></h2>
<ul class="simple">
<li>Advertisement and discovery of selector services implemented by a node</li>
<li>Implementation overhead (processing, etc) for a Member Node</li>
<li>Representation formats for extracted information</li>
<li>Access control policies (managed parent object controls everything?)</li>
</ul>
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<h3><a href="../index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Selectors for Data Package Components</a><ul>
<li><a class="reference internal" href="#goal">Goal</a></li>
<li><a class="reference internal" href="#rationale">Rationale</a></li>
<li><a class="reference internal" href="#implications-for-implementation">Implications for Implementation</a></li>
</ul>
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