[AMF] docs

dhp-workflows/dhp-actionmanager/README.md

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+# Action Management Framework
+
+This module implements the oozie workflow for the integration of pre-built contents into the OpenAIRE Graph.
+
+Such contents can be 
+
+* brand new, non-existing records to be introduced as nodes of the graph
+* updates (or enrichment) for records that does exist in the graph (e.g. a new subject term for a publication)
+* relations among existing nodes
+
+The actionset contents are organised into logical containers, each of them can contain multiple versions contents and is characterised by
+
+* a name
+* an identifier
+* the paths on HDFS where each version of the contents is stored
+
+Each version is then characterised by 
+
+* the creation date
+* the last update date
+* the indication where it is the latest one or it is an expired version, candidate for garbage collection
+
+## ActionSet serialization
+
+Each actionset version contains records compliant to the graph internal data model, i.e. subclasses of `eu.dnetlib.dhp.schema.oaf.Oaf`,
+defined in the external schemas module
+
+```
+<dependency>
+    <groupId>eu.dnetlib.dhp</groupId>
+    <artifactId>${dhp-schemas.artifact}</artifactId>
+    <version>${dhp-schemas.version}</version>
+</dependency>
+```
+
+When the actionset contains a relationship, the model class to use is `eu.dnetlib.dhp.schema.oaf.Relation`, otherwise 
+when the actionset contains an entity, it is a `eu.dnetlib.dhp.schema.oaf.OafEntity` or one of its subclasses 
+`Datasource`, `Organization`, `Project`, `Result` (or one of its subclasses `Publication`, `Dataset`, etc...). 
+
+Then, each OpenAIRE Graph model class instance must be wrapped using the class `eu.dnetlib.dhp.schema.action.AtomicAction`, a generic 
+container that defines two attributes
+
+* `T payload` the OpenAIRE Graph class instance containing the data;
+* `Class<T> clazz` must contain the class whose instance is contained in the payload.
+
+Each AtomicAction can be then serialised in JSON format using `com.fasterxml.jackson.databind.ObjectMapper` from
+
+```
+<dependency>
+    <groupId>com.fasterxml.jackson.core</groupId>
+    <artifactId>jackson-databind</artifactId>
+    <version>${dhp.jackson.version}</version>
+</dependency>
+```
+
+Then, the JSON serialization must be stored as a GZip compressed sequence file (`org.apache.hadoop.mapred.SequenceFileOutputFormat`). 
+As such, it contains a set of tuples, a key and a value defined as `org.apache.hadoop.io.Text` where
+
+* the `key` must be set to the class canonical name contained in the `AtomicAction`;
+* the `value` must be set to the AtomicAction JSON serialization.
+
+The following snippet provides an example of how create an actionset version of Relation records:
+
+```
+  rels // JavaRDD<Relation>
+    .map(relation -> new AtomicAction<Relation>(Relation.class, relation))
+    .mapToPair(
+        aa -> new Tuple2<>(new Text(aa.getClazz().getCanonicalName()),
+            new Text(OBJECT_MAPPER.writeValueAsString(aa))))
+    .saveAsHadoopFile(outputPath, Text.class, Text.class, SequenceFileOutputFormat.class, GzipCodec.class);
+```
+