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Note that the name of the relationship reflects the direction, i.e. pointing from <code>Group</code> to <code>User</code>.
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This is due to the fact that the actual metadata aspect holding this information is associated with <code>Group</code>, rather than
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User.
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Had the direction been reversed, the relationship would have been named <code>IsMemberOf</code> instead.
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See <a href="#direction-of-relationships">Direction of Relationships</a> for more discussions on relationship directionality.
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A specific instance of a relationship, e.g. <code>urn:li:corpGroup:group1</code> has a member <code>urn:li:corpuser:user1</code>,
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corresponds to an edge in the metadata graph.</p><p>Relationships are meant to be "entity-neutral". In other words, one would expect to use the same <code>OwnedBy</code> relationship
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to link a <code>Dataset</code> to a <code>User</code> and to link a <code>Dashboard</code> to a <code>User</code>.
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As Pegasus doesn’t allow typing a field using multiple URNs (because they’re all essentially strings), we resort to
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using generic URN type for the source and destination.
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We also introduce a <code>@Relationship</code> <a href="/docs/metadata-modeling/extending-the-metadata-model/#relationship">annotation</a> to
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limit the allowed source and destination URN types.</p><p>While it’s possible to model relationships in rest.li
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as <a href="https://linkedin.github.io/rest.li/modeling/modeling#association" target="_blank" rel="noopener noreferrer">association resources</a>, which often get stored as
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mapping tables, it is far more common to model them as "foreign keys" field in a metadata aspect. For instance,
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the <code>Ownership</code> aspect is likely to contain an array of owner’s corpUser URNs.</p><p>Below is an example of how a relationship is modeled in PDL. Note that:</p><ol><li>This aspect, <code>nativeGroupMembership</code> would be associated with a <code>corpUser</code></li><li>The <code>corpUser</code>'s aspect points to one or more parent entities of type <code>corpGroup</code></li></ol><div class="codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-text codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token plain">namespace com.linkedin.identity</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">import com.linkedin.common.Urn</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">/**</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> * Carries information about the native CorpGroups a user is in.</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> */</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">@Aspect = {</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> "name": "nativeGroupMembership"</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">}</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">record NativeGroupMembership {</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> @Relationship = {</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> "/*": {</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> "name": "IsMemberOfNativeGroup",</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> "entityTypes": [ "corpGroup" ]</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> }</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> }</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> nativeGroups: array[Urn]</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="direction-of-relationships">Direction of Relationships<a href="#direction-of-relationships" class="hash-link" aria-label="Direct link to Direction of Relationships" title="Direct link to Direction of Relationships"></a></h2><p>As relationships are modeled as directed edges between nodes, it’s natural to ask which way should it be pointing,
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||
or should there be edges going both ways? The answer is, "doesn’t really matter." It’s rather an aesthetic choice than
|
||
technical one.</p><p>For one, the actual direction doesn’t really impact the execution of graph queries. Most graph DBs are fully capable of
|
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traversing edges in reverse direction efficiently.</p><p>That being said, generally there’s a more "natural way" to specify the direction of a relationship, which closely relate
|
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to how the metadata is stored. For example, the membership information for an LDAP group is generally stored as a list
|
||
in group’s metadata. As a result, it’s more natural to model a <code>HasMember</code> relationship that points from a group to a
|
||
member, instead of a <code>IsMemberOf</code> relationship pointing from member to group.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="high-cardinality-relationships">High Cardinality Relationships<a href="#high-cardinality-relationships" class="hash-link" aria-label="Direct link to High Cardinality Relationships" title="Direct link to High Cardinality Relationships"></a></h2><p>See <a href="/docs/advanced/high-cardinality">this doc</a> for suggestions on how to best model relationships with high
|
||
cardinality.</p></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="slackUtm_uoBr"><div class="slackUtm_uoBr"><hr>Need more help? 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