immutability en Immutability and Event Derivation in RDF <span property="schema:name" class="field field-node--title field-name-title field-type-string field-label-hidden">Immutability and Event Derivation in RDF</span> <span rel="schema:author" class="field field-node--uid field-name-uid field-type-entity-reference field-label-hidden"><a title="View user profile." href="/users/rolandstuehmer" lang="" about="/users/rolandstuehmer" typeof="schema:Person" property="schema:name" datatype="" class="username">roland.stuehmer</a></span> <span property="schema:dateCreated" content="2014-10-01T14:54:13+00:00" class="field field-node--created field-name-created field-type-created field-label-hidden">Wed, 10/01/2014 - 16:54</span> <div property="schema:text" class="clearfix field field-node--body field-name-body field-type-text-with-summary field-label-hidden"> <div class="field-items"> <div property="schema:text" class="field-item"><p>"In many event processing systems [...] events are immutable"<sup id="fnref:Luckham and Schulte 2011"><a href="#fn:Luckham and Schulte 2011" class="footnote-ref">1</a></sup>. This stems from the definition of what an event is: "An event is an occurrence within a particular system or domain; it is something that has happened, or is contemplated as having happened [...]"<sup id="fnref:Etzion and Niblett 2010"><a href="#fn:Etzion and Niblett 2010" class="footnote-ref">2</a></sup>. So events cannot be made to unhappen.</p> <p><strong>Open Question:</strong> Does this apply to all systems/applications/usecases or just to "many" as stated above?</p> <p>I made immutability a <strong>general assumption</strong> in my work<sup id="fnref:Stühmer 2014"><a href="#fn:Stühmer 2014" class="footnote-ref">3</a></sup>. It is very useful for building systems (distributed systems, consistency, ...).</p> <p><strong>Q: How can a Stream processing agent process events if they are immutable?</strong></p> <p><strong>A:</strong> Every processing task produces new <em>derived events</em> as results. Advantage: the underived events are still available for other uses and remain immutable.</p> <p>For <abbr title="RDF Stream Processing">RSP</abbr> this means: (1) create a new (unique) graph for the derived event (2) possibly link back to the base event(s) thus enabling drill-down or root cause / provenance analysis of the derived event. The links can be made with <code>DUL:hasConstituent</code> from DOLCE Ultralight<sup id="fnref:Gangemi 2009"><a href="#fn:Gangemi 2009" class="footnote-ref">4</a></sup>. In my own work<sup id="fnref:Harth and Stühmer 2011"><a href="#fn:Harth and Stühmer 2011" class="footnote-ref">5</a></sup> I use a new <code>:members</code> property to link from a derived event to its simple events. The property is a subproperty of the mentioned <code>DUL:hasConstituent</code>.</p> <p><strong>Observation:</strong> We talk about adding "received time" and other metadata later by receiving agents: Adding triples later to the event graph with graphname as subject can still be legal and considered as <em>amending</em> the event header. Much like with email: headers can be added by intermediate mail servers but the mail body and ID are immutable.</p> <div class="footnotes"> <hr /> <ol> <li id="fn:Luckham and Schulte 2011"> <p>Luckham, D. C. &amp; Schulte, R. <a href="">Event Processing Glossary - Version 2.0 (2011)</a>&#160;<a href="#fnref:Luckham and Schulte 2011" class="footnote-backref">&#8617;&#xFE0E;</a></p> </li> <li id="fn:Etzion and Niblett 2010"> <p>Etzion, O. &amp; Niblett, P. Event Processing in Action Manning Publications Co. (2010)&#160;<a href="#fnref:Etzion and Niblett 2010" class="footnote-backref">&#8617;&#xFE0E;</a></p> </li> <li id="fn:Stühmer 2014"> <p>Stühmer, R. <a href="">Web-oriented Event Processing Karlsruhe Institute of Technology, KIT Scientific Publishing, Karlsruhe, 2014</a>&#160;<a href="#fnref:Stühmer 2014" class="footnote-backref">&#8617;&#xFE0E;</a></p> </li> <li id="fn:Gangemi 2009"> <p>Gangemi, A. <a href="">DOLCE+DnS Ultralite (<abbr title="DOLCE+DnS Ultralite">DUL</abbr>) (2009)</a>&#160;<a href="#fnref:Gangemi 2009" class="footnote-backref">&#8617;&#xFE0E;</a></p> </li> <li id="fn:Harth and Stühmer 2011"> <p>Harth, A. &amp; Stühmer, R. <a href="">Publishing Event Streams as Linked Data Karlsruhe Institute of Technology, FZI Forschungszentrum Informatik (2011)</a>&#160;<a href="#fnref:Harth and Stühmer 2011" class="footnote-backref">&#8617;&#xFE0E;</a></p> </li> </ol> </div> </div> </div> </div> <section class="field field-node--comment-node-article field-name-comment-node-article field-type-comment field-label-hidden comment-wrapper"> </section> <div class="field field-node--field-tags field-name-field-tags field-type-entity-reference field-label-inline clearfix"> <div class="field-label">Tags</div> <div class="field-items"> <div class="field-item"><a href="/tags/immutability" property="schema:about" hreflang="en">immutability</a></div> <div class="field-item"><a href="/tags/rdf" property="schema:about" hreflang="en">RDF</a></div> <div class="field-item"><a href="/tags/rsp" property="schema:about" hreflang="en">RSP</a></div> <div class="field-item"><a href="/tags/stream" property="schema:about" hreflang="en">stream</a></div> <div class="field-item"><a href="/tags/event-derivation" property="schema:about" hreflang="en">event derivation</a></div> </div> </div> Wed, 01 Oct 2014 14:54:13 +0000 roland.stuehmer 39 at