SAVOT - Simple Access to VOTable - Release 2.6

1. SAVOT - Simple Access to VOTable - Release 2.6
   1. Introduction
   2. The Data model
   3. The Pull parsing mode (packages : cds.savot.pull, cds.savot.model and cds.savot.common)
   4. The SAXLike parsing mode (package : cds.savot.sax and cds.savot.common, cds.savot.model is optional)
   5. Quick start with SAVOT Pull !
      1. Example 1 : FULL mode
      2. Example 2 : SEQUENTIAL mode
   6. Quick start with SAVOT SAXLike !
      1. Example : SAVOT SAX
   7. FAQ
   8. Statistics (SAVOT Pull)
   9. Download and links

Introduction

• to provide Java VOTable parsers based on different parsing models
• to provide small Java VOTable parsers which can be included in applets

• SAVOT is a generic name for our work
• SAVOT Pull is the parser based on the pull parsing method
• SAVOT SAX is the parser based on the SAX parsing method

The Data model

The Pull parsing mode (packages : cds.savot.pull, cds.savot.model and cds.savot.common)

• The FULL mode loads the whole XML document into the memory (internal data model cds.savot.model).

• The SEQUENTIAL mode loads an XML document RESOURCE per RESOURCE into the memory and unload the previous RESOURCE.

Usefull informations about the work which is done around the pull parsing method.

The SAXLike parsing mode (package : cds.savot.sax and cds.savot.common, cds.savot.model is optional)

In some use cases, it can be important to use a SAX parsing mode because it is possible to execute actions in the different steps of the parsing.

Quick start with SAVOT Pull !

* The usual questions...

Which packages ?

• cds.savot.model to put information in the memory
• cds.savot.pull for the VOTable parsing
• cds.savot.common common things used for all modes
• kxml2-min for the XML parsing
• cds.savot.writer (optional) if you want de create VOTable documents (edition or creation from scratch)

And the CLASSPATH ?

Put the four above packages in the CLASSPATH

Does it work ?

Download one of the samples and execute it

If it works, cheers, if not goto *

To start a basic source code, you must choose in which mode, FULL or SEQUENTIAL, you want to parse the VOTable file.

Example 1 : FULL mode

      // the whole VOTable file is put into memory
      SavotPullParser sb = new SavotPullParser(source, SavotPullEngine.FULL); !!! parsing of  the whole source 
 
      System.out.println("Resource name : " + ((SavotResource)sb.getVOTable().getResources().getItemAt(0)).getName());

      // get the VOTable object
      SavotVOTable sv = sb.getVOTable(); !!! sv is now a reference to a VOTable object
      
	try {
        BufferedWriter bw = null;

        if (target != null) {
          bw = new BufferedWriter(new FileWriter(target));
        }

        // for each resource
        for (int l = 0; l < sb.getResourceCount(); l++) {
 
          SavotResource currentResource = (SavotResource)(sv.getResources().getItemAt(l));

          // for each table of the current resource
          for (int m = 0; m < currentResource.getTableCount(); m++) {

            // get all the rows of the table
            TRSet tr = currentResource.getTRSet(m);

            System.out.println("Number of items in TRset (= number of <TR></TR>) : " + tr.getItemCount());

            // for each row
            for (int i = 0; i < tr.getItemCount(); i++) {

              // get all the data of the row
              TDSet theTDs = tr.getTDSet(i);
              String currentLine = new String();
              System.out.println("Number of items in TDSet for the index " + (i+1) + " tr (= number of <TD></TD>) : " + theTDs.getItemCount());

              // for each data of the row
              for (int j = 0; j < theTDs.getItemCount(); j++) {
                currentLine = currentLine + theTDs.getContent(j);
                System.out.println("<"+theTDs.getContent(j)+">");
              }

              if (target != null) {
                if (target.compareTo("") != 0) {
                  bw.write(currentLine);
                  bw.newLine();
              }
            }
            else
              System.out.println(currentLine);
          }
        }
        if (target != null) {
          bw.flush();
          bw.close();
        }
      }
    }	...

! If you want to try this example, execute the PullFullSample2 class

Example 2 : SEQUENTIAL mode

In this example we show how to use the SEQUENTIAL mode

    // begin the parsing
    SavotPullParser sb = new SavotPullParser(source, SavotPullEngine.SEQUENTIAL);!!! parsing starting 
    
    // get the next resource of the VOTable file
    SavotResource currentResource = sb.getNextResource();  !!! get the next resource

    // while a resource is available
    while (currentResource != null) {

      // for each table of this resource
      for (int i = 0; i < currentResource.getTableCount(); i++) {
        tr = currentResource.getTRSet(i);

        if (tr != null) {
          System.out.println("Number of items in TRset (= number of <TR></TR>) : " + tr.getItemCount());

          // for each row of the table
          for (int j = 0; j < tr.getItemCount(); j++) {

            // get all the data of the row
            TDSet theTDs = tr.getTDSet(j);

            String currentLine = new String();

            System.out.println("Number of items in TDSet for the index " + (j+1) + " tr (= number of <TD></TD>) : " + theTDs.getItemCount());

            // for each data of the row
            for (int k = 0; k < theTDs.getItemCount(); k++) {
              currentLine = currentLine + theTDs.getContent(k);
              System.out.println("<" + theTDs.getContent(k) + ">");
            }
          }
        }
      }
      // get the next resource
      currentResource = sb.getNextResource();
    }
! If you want to try this example, execute the PullSeqSample class 

Quick start with SAVOT SAXLike !

Which packages ?

• cds.savot.sax for the VOTable parsing
• cds.savot.common common things used for all modes
• kxml2-min for the XML parsing
• cds.savot.model (optional) to put information in the memory (you can use your own data model)

You can download these packages in the Download corner

And the CLASSPATH ?

Put the above packages in the CLASSPATH

• a FIELD element starts
• a content is present between <TD>..</TD>

Example : SAVOT SAX

import java.util.Vector;import cds.savot.sax.*;public class SavotSAXSample implements SavotSAXConsumer {  public SavotSAXSample() {
  }  // attributes is a Vector containing couples of (attribute name, attribute value)
  // exemple : (attributes.elementAt(0), attributes.elementAt(1)), (attributes.elementAt(2), attributes.elementAt(3)), ...

  /**
   *
   * @param attributes Vector
   */
  public void showAttributes(Vector attributes) {    for (int i = 0; i < attributes.size(); i = i + 2) {
      System.out.println("Attribute name : " + attributes.elementAt(i) + " Attribute value : " + attributes.elementAt(i + 1));
    }
  }  // start elements
  public void startVotable(Vector attributes) {
    showAttributes(attributes);
  }  public void startDescription(){
  }  public void startResource(Vector attributes){
    showAttributes(attributes);
  }  public void startTable(Vector attributes){
  }
  
...  // end elements

   public void endVotable(){}   public void endDescription(){}   public void endResource(){}   public void endTable(){}

...   // TEXT

   public void textTD(String text){ 
     System.out.println(text);
   }   public void textMin(String text){}   public void textMax(String text){}

...   // document
   public void startDocument(){}   public void endDocument(){}
}

 The following lines must be included in your application :
...
    SavotSAXSample consumer = new SavotSAXSample();
    SavotSAXParser sb = new SavotSAXParser(consumer, file);
...
The SavotSaxSample consumer will be taken into account during the parsing process.

FAQ

• Parsers which implements DOM need often very large memory size (20 times the XML document size and it is not a joke !!), so we decided to use a pull parser to load the document in our own data model.

Q : Why different parsers ?

• We need parsers for different use cases, sometimes for very small applications, so we cannot use a 2MB parser which would be 10 times bigger than the application itself !!! Sometimes it is very interesting to load all the document in the memory and sometimes it is better to use a SAX parser. It depends on what you want really to do.

Statistics (SAVOT Pull)

• Laptop Intel Pentium 4M 2.2GHz
• 512 DDR MB
• 40 GB HD

• Microsoft Windows XP SP2 (*)
• Sun JDK 1.4.2 release 6 (**)

These tests have been done with the pull parser kXML

All the VOTable document is loaded into the SAVOT internal data model and is available in memory for access through the API

Download and links

Download corner

Here we have put some links pointing to XML parsers which have been tested

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