[dna-issues] [JBoss JIRA] Commented: (DNA-37) Federate schema information from relational sources

[Sergiy Litsenko (JIRA)]

    [ https://jira.jboss.org/jira/browse/DNA-37?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12439191#action_12439191 ] 

Sergiy Litsenko commented on DNA-37:
------------------------------------

>From Randall: Let's table the data discussion for the moment. 
>From Sergiy:
I agree  - we have plenty of work to do with database metadata integration with Connector on its own. 
But before I forgot I'm posting the following reference links that might be ususeful for future discussions/decisions about data paging and sampling (may be similar to Google (search for 'java' term returns "Results 1 - 10 of about 368,000,000 for java") 

it is related to several layers - not just the connector for relational sources: - JCR spec and our implementation, REST access / Atom publishing.

>From JBoss DNA Graph API prospective:

            package org.jboss.dna.graph.requests
                    ReadBlockOfChildrenRequest
                                    startingIndex the index of the first child to be included in the block
                                    count the maximum number of children that should be included in the block

                    ReadNextBlockOfChildrenRequest
                                    startingAfter the child that was the last child of the previous block of children read
                                    count the maximum number of children that should be included in the block
>From JCR prospective,  JSR-170: 
             6.2.3 Node Read Methods
                          public interface Node extends Item {
                                     NodeIterator getNodes(); // Returns all child nodes of this node.
                          }

                           public interface NodeIterator extends RangeIterator {}

                            public interface RangeIterator extends Iterator {
                                      public long getSize(); // the number of elements in the iterator
                                      public long getPosition(); // current position within the iterator
                                      public void skip(long skipNum); // Skip a number of elements in the iterator
                           }

             6.6.12 Query Results
                           javax.jcr.query.QueryResult:
                                      RowIterator getRows(); // query result as an iterator

                          public interface RowIterator extends RangeIterator {}


>From  Java Persistence 1.0 prospective (if persistence of graph implemented using JPA):
                 public interface Query {
                              setMaxResults(int maxResult);// Set the maximum number of results to retrieve.
                              setFirstResult(int startPosition) ; // Set the position of the first result to retrieve.
                 }

>From Atom Syndication format prospective:

While feed paging is not directly supported by http://www.ietf.org/rfc/rfc4287.txt  (correct me if I wrong) it might be useful implementing data paging using 'rel' attribute of the <link>element. Some example described here: http://www.ibm.com/developerworks/library/x-tipatom2/  "Paging Atom: Create a multi-section Atom collection or feed". See an example below for Atom + OpenSearch combined.

 From Open Search prospective (http://www.opensearch.org/Specifications/OpenSearch/1.1 and http://en.wikipedia.org/wiki/OpenSearch):

         OpenSearch 1.1 parameters:
                The "count" parameter - Replaced with the number of search results per page desired by the search client. 
                The "startIndex" parameter  - Replaced with the index of the first search result desired by the search client. 
                The "startPage" parameter - Replaced with the page number of the set of search results desired by the search client. 

          An example for Atom + OpenSearch combined:
                   <feed xmlns="http://www.w3.org/2005/Atom" 
                               xmlns:opensearch="http://a9.com/-/spec/opensearch/1.1/">
                              <opensearch:Query role="request" searchTerms="JBoss DNA"  startPage="1"/>
                               <opensearch:totalResults>12345</opensearch:totalResults>
                               <opensearch:startIndex>21</opensearch:startIndex>
                               <opensearch:itemsPerPage>10</opensearch:itemsPerPage>

                               <link rel="self" type="application/atom+xml" href="http://www.jboss.org/dna/atomFeed"/>
                               <link rel="first" href="http://www.jboss.org/dna/atomFeed"/>
                               <link rel="next" href="http://www.jboss.org/dna/atomFeed?page=2"/>
                               <link rel="last" href="http://www.jboss.org/dna/atomFeed?page=123"/>
                               
                            <entry>...</entry>
                            <entry>...</entry>
                    </feed>



> Federate schema information from relational sources
> ---------------------------------------------------
>
>                 Key: DNA-37
>                 URL: https://jira.jboss.org/jira/browse/DNA-37
>             Project: DNA
>          Issue Type: Feature Request
>          Components: Connectors
>            Reporter: Randall Hauch
>            Assignee: Sergiy Litsenko
>            Priority: Minor
>             Fix For: 0.4
>
>
> Create a connector for the federation engine that contributes and exposes the database schema information for a relational database (via JDBC) into the federated repository.  This would make it possible to have a repository provide information about the databases in an organization.  One choice would be whether to import (and copy) the schema structure, or to provide access to it in real time.

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