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## org.eclipse.lyo.core.trs
Class ChangeLog

    java.lang.Object
      org.eclipse.lyo.oslc4j.core.model.AbstractResource
          org.eclipse.lyo.core.trs.AbstractChangeLog
              org.eclipse.lyo.core.trs.ChangeLog

All Implemented Interfaces:
  IExtendedResource, IResource

    public class ChangeLog

extends AbstractChangeLog

A Change Log provides a list of changes. The following example illustrates the contents of a Change Log:

     # Resource: http://cm1.example.com/trackedResourceSet
     @prefix trs: <http://open-services.net/ns/core/trs#> .
     @prefix xsd: <http://www.w3.org/2001/XMLSchema#> .

     <http://cm1.example.com/trackedResourceSet>
       a trs:TrackedResourceSet ;
       trs:base <http://cm1.example.com/baseResources> ;
       trs:changeLog [
         a trs:ChangeLog ;
         trs:change <urn:urn-3:cm1.example.com:2010-10-27T17:39:33.000Z:103> ;
         trs:change <urn:urn-3:cm1.example.com:2010-10-27T17:39:32.000Z:102> ;
         trs:change <urn:urn-3:cm1.example.com:2010-10-27T17:39:31.000Z:101> .
       ] .

     <urn:urn-3:cm1.example.com:2010-10-27T17:39:33.000Z:103>
       a trs:Creation ;
       trs:changed <http://cm1.example.com/bugs/23> ;
       trs:order "103"^^xsd:integer .

     <urn:urn-3:cm1.example.com:2010-10-27T17:39:32.000Z:102>
       a trs:Modification ;
       trs:changed <http://cm1.example.com/bugs/22> ;
       trs:order "102"^^xsd:integer .

     <urn:urn-3:cm1.example.com:2010-10-27T17:39:31.000Z:101>
       a trs:Deletion ;
       trs:changed <http://cm1.example.com/bugs/21> ;
       trs:order "101"^^xsd:integer .

As shown, a Change Log provides a set of Change Event entries in a multi-valued RDF property called trs:change.

Change Events MUST have URIs (i.e., they cannot be Blank Nodes) to allow Clients to recognize entries they have seen before. The URI is only used to identify an event (i.e., it need not be HTTP GETable).

Each Change Event has a sequence number, trs:order; sequence numbers are non-negative integer values that increase over time. A Change Event entry carries the URI of the changed Resource, trs:changed, and an indication, via rdf:type (a.k.a. "a" in Turtle), of whether the Resource was added to the Resource Set, removed from the Resource Set, or changed state while a member of the Resource Set. The entry with the highest trs:order value (i.e., 103 in this example) is the most recent change. As changes continue to occur, a Server MUST add new Change Events to the newest Change Log segment. The sequence number (i.e., trs:order) of newer entries MUST be greater than previous ones. The sequence numbers MAY be consecutive numbers but need not be.

Note that the actual time of change is not included in a Change Event. Only a sequence number, representing the "sequence in time" of each change is provided. The URI of a Change Event MUST be guaranteed unique, even in the wake of a Server roll back where sequence numbers get reused. A time stamp MAY be used to generate such a URI, as in the above example, although other ways of generating a unique URI are also possible.

A Change Log represents a series of changes to its corresponding Resource Set over some period of time. The Change Log MUST contain Change Events for every Resource creation, deletion, and modification during that period. A Server MUST report a Resource modification event if a GET on it would return a semantically different response from previously. For a resource with RDF content, a modification is anything that would affect the set of RDF triples in a significant way. A Server MAY safely report a modification event even in cases where there would be no significant difference in response. Some cases of modifications that would be considered semantically different from previous or significant difference would be: inserted triple, removed triple, triple replaced (new object/literal, e.g. changing boolean literal "true" to "false"), replaced vocabulary term used (e.g. change from dcterms:title to rdfs:label).

The Server SHOULD NOT report unnecessary Change Events although it might happen, for example, if changes occur while the base is being computed. A Client SHOULD ignore a creation event for a Resource that is already a member of the Resource Set, and SHOULD ignore a deletion or modification event for a Resource that is not a member of the Resource Set.

Constructor Summary
`ChangeLog()`

Method Summary
`List<ChangeEvent>` | `getChange()`
`URI` | `getPrevious()`
`void` | `setChange(List<ChangeEvent> change)`
`void` | `setPrevious(URI previous)`

Methods inherited from class org.eclipse.lyo.oslc4j.core.model.AbstractResource
`addType, getAbout, getExtendedProperties, getTypes, setAbout, setExtendedProperties, setTypes`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### ChangeLog

    public ChangeLog()

Method Detail

### getChange

    public List<ChangeEvent> getChange()

  Returns:
    the change

### setChange

    public void setChange(List<ChangeEvent> change)

  Parameters:
    `changes` - the changes to set

### getPrevious

    public URI getPrevious()

  Returns:
    the previous

### setPrevious

    public void setPrevious(URI previous)

  Parameters:
    `previous` - the previous to set

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