Metacat

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Metacat Server provides functionality for inserting, updating, and deleting XML documents in the database. Inserted or updated documents are read, checked for validity, decomposed into nodes and inserted into the db. Document validity is checked if a valid DTD is provided.

architecture diagram of write action

Operations

INSERT - A new XML document is inserted into the DB with given unique docid. The client must specify the docid.
UPDATE - A document is provided to update a document that already has a valid docid. The original document is archived, then overwritten.
DELETE - Document is archived, and pointer in xml_documents is moved to xml_revisions, efectively deleting the document from public view but preserving the revision for the revision history.

Insertions, updates and deletes are passed to Metacat as servlet parameters. The following is an example of a web form that can perform these tasks.

    <html>
    <head>
    <title>MetaCat</title>
    <link rel="stylesheet" type="text/css" href="metacat/style/rowcol.css">
    </head>
    <body class="emlbody">
    <b>MetaCat XML Loader</b>
    <p>
    Upload, Change, or Delete an XML document using this form.
    </p>
    <form action="http://dev.nceas.ucsb.edu/metacat/servlet/metacat" method="POST">
      <strong>1. Choose an action: </strong>
      <input type="radio" name="action" value="insert" checked> Insert
      <input type="radio" name="action" value="update"> Update
      <input type="radio" name="action" value="delete"> Delete
      <input type="submit" value="Process Action">
      <br />
      <strong>2. Provide a Document ID </strong>
      <input type="text" name="docid"> (optional for Insert)
         <input type="checkbox" name="public" value="yes" checked><strong>Public Document</strong>
      <br />
      <strong>3. Provide XML text </strong> (not needed for Delete)
      <textarea name="doctext" cols="65" rows="15"></textarea>
      <strong>4. Provide DTD text for upload </strong> (optional; not needed for Delete)
      <textarea name="dtdtext" cols="65" rows="15"></textarea>
    </form>
    </body>
    </html>

Once inserted into the database, the document looks like the following:

SQL> select * from xml_nodes where docid='NCEAS:1' 

NODEID NODEINDEX NODETYPE   NODENAME        NODEDATA               PARENTNODEID ROOTNODEID DOCID  
------ --------- ---------- --------------- ---------------------- ------------ ---------- -------
     1           DOCUMENT   eml-dataset                                                  1 NCEAS:1
     2         1 ELEMENT    eml-dataset                                       1          1 NCEAS:1
     3         1 TEXT                                                         2          1 NCEAS:1


     4         2 ELEMENT    meta_file_id                                      2          1 NCEAS:1
     5         1 TEXT                       NCEAS:1                           4          1 NCEAS:1
     6         3 TEXT                                                         2          1 NCEAS:1


     7         4 ELEMENT    dataset_id                                        2          1 NCEAS:1
     8         1 TEXT                       Dist.ssd01                        7          1 NCEAS:1
     9         5 TEXT                                                         2          1 NCEAS:1


    10         6 ELEMENT    title                                             2          1 NCEAS:1
    11         1 TEXT                       Insights on community            10          1 NCEAS:1
                                            dynamics

    12         7 TEXT                                                         2          1 NCEAS:1


    13         8 ELEMENT    originator                                        2          1 NCEAS:1
    14         1 ATTRIBUTE  description     Names and addresses of           13          1 NCEAS:1
                                            principal investigator

If you follow the parentnodeid pointers you can recontruct this document. The Metacat Database section provides more details on the storage of XML documents.

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