- add dataset references and identifiers

Database.md

@@ -82,5 +82,21 @@ TETHYS stores metadata about all files in a separate database table ('document_f
 TETHYS RDR calculates internal checksums during the ingestion workflow. These checksums ensure that ingested data has not been altered or damaged. A checksum is a short sequence of bits or bytes that is calculated from the data using an algorithm. If even a single bit of the data changes, the checksum will also change, indicating that the data has been changed unintentionally on the file store. During the file upload, TETHYS calculates and stores md5 and sha512-checksums for each file (see attribute type).
 
 * **document_licences** with pivot table 'link_document_licences':
-Creative Commons licenses are commonly used to govern the use and distribution of research data. For example, a researcher might choose to make their research data available under a CC-BY license, which allows others to share, adapt, and build upon the data as long as they provide attribution to the original author. All preferred CC licences for TETHYS are described in the manual [Manual p15](https://tethys.at/docs/HandbuchTethys.pdf#page=16).
+Creative Commons licenses are commonly used to govern the use and distribution of research data. For example, a researcher might choose to make their research data available under a CC-BY license, which allows others to share, adapt, and build upon the data as long as they provide attribution to the original author. All preferred CC licences for TETHYS are described in the manual [manual, p. 15](./docs/HandbuchTethys.pdf#page=16).
+
+
+## Dataset references & identifiers
+During the ingestion of the new dataset, there is the possibility to refer to existing publications (table 'document_references') through persistent Identifier (PID). Such identifiers are precisely defined and described in Tethys RDR under the metadata element "Dataset References" as identifier types: DOI, HANDLE, ISBN, URL, and URN. [manual, p. 21](./docs/HandbuchTethys.pdf#page=22). Self referencing identifiers of a dataset are stored inside the table 'document_identifiers'.
+
+In addition, the relation types (the kind of relationship) are precisely defined [manual, p. 22](./docs/HandbuchTethys.pdf#page=23). In most cases, the relation type “IsNewVersionOf” will be used.
+
+![title](./tethys_references.png)
+* **document_identifiers**:
+    * 'type': allowed values are: 'doi', 'handle', 'isbn', 'issn', 'url' and 'urn'
+    * 'value': for example der url of a doi
+* **document_references**:
+    * 'type': allowed values are: 'DOI', 'Handle', 'ISBN', 'ISSN','URL' and  'URN'
+    * 'value': for example der url of a doi
+    * 'relation': the following relation types are allowed in TETHYS: 'IsSupplementTo', 'IsSupplementedBy', 'IsContinuedBy', 'Continues', 'IsNewVersionOf', 'IsPartOf', 'HasPart', 'Compiles', 'IsVariantFormOf'
+
 

docs/HandbuchTethys.pdf:Zone.Identifier

@@ -0,0 +1,3 @@
+[ZoneTransfer]
+ZoneId=3
+HostUrl=about:internet