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Revision 1.3: download - view: text, annotated - select for diffs
Thu Apr 7 06:56:22 2005 UTC (19 years, 8 months ago) by albertel
Branches: MAIN
CVS tags: version_2_9_X, version_2_9_99_0, version_2_9_1, version_2_9_0, version_2_8_X, version_2_8_99_1, version_2_8_99_0, version_2_8_2, version_2_8_1, version_2_8_0, version_2_7_X, version_2_7_99_1, version_2_7_99_0, version_2_7_1, version_2_7_0, version_2_6_X, version_2_6_99_1, version_2_6_99_0, version_2_6_3, version_2_6_2, version_2_6_1, version_2_6_0, version_2_5_X, version_2_5_99_1, version_2_5_99_0, version_2_5_2, version_2_5_1, version_2_5_0, version_2_4_X, version_2_4_99_0, version_2_4_2, version_2_4_1, version_2_4_0, version_2_3_X, version_2_3_99_0, version_2_3_2, version_2_3_1, version_2_3_0, version_2_2_X, version_2_2_99_1, version_2_2_99_0, version_2_2_2, version_2_2_1, version_2_2_0, version_2_1_X, version_2_1_99_3, version_2_1_99_2, version_2_1_99_1, version_2_1_99_0, version_2_1_3, version_2_1_2, version_2_1_1, version_2_1_0, version_2_12_X, version_2_11_X, version_2_11_5_msu, version_2_11_5, version_2_11_4_uiuc, version_2_11_4_msu, version_2_11_4, version_2_11_3_uiuc, version_2_11_3_msu, version_2_11_3, version_2_11_2_uiuc, version_2_11_2_msu, version_2_11_2_educog, version_2_11_2, version_2_11_1, version_2_11_0_RC3, version_2_11_0_RC2, version_2_11_0_RC1, version_2_11_0, version_2_10_X, version_2_10_1, version_2_10_0_RC2, version_2_10_0_RC1, version_2_10_0, version_2_0_X, version_2_0_99_1, version_2_0_2, version_2_0_1, version_2_0_0, version_1_99_3, version_1_99_2, version_1_99_1_tmcc, version_1_99_1, version_1_99_0_tmcc, version_1_99_0, loncapaMITrelate_1, language_hyphenation_merge, language_hyphenation, bz6209-base, bz6209, bz5969, bz2851, PRINT_INCOMPLETE_base, PRINT_INCOMPLETE, HEAD, GCI_3, GCI_2, GCI_1, BZ5971-printing-apage, BZ5434-fox, BZ4492-merge, BZ4492-feature_horizontal_radioresponse
- ENV -> env

<html>
<head>
</head>
<body bgcolor='#ffffff'>
<a name='helptop' />
<img align='right' src='/adm/lonIcons/lonhelplogos.gif' />
<h1>Search Catalog</h1>
<hr />
<form>
<input type='button' onClick='self.close()' value='Close this help window' />
</form>
<ol>
<li><a href='#queryconstruct'>Constructing a query</a></li>
<li><a href='#scanningstatus'>Understanding the Search Progress screen</a></li>
<li><a href='#outputview'>Viewing the Output of Search Results</a>
<li><a href='#controlwho'>Controlling who can search through resources</a></li>
<li><a href='#engineperformance'>Search engine performance measurements</a>
</li>
<li><a href='#softwarearchitecture'>Notes on software architecture</a></li>
<li><a href='#limitations'>Limitations</a></li>
</ol>
<a name='queryconstruct' />
<a href='#helptop'>
<img border='0' align='left' src='/adm/lonIcons/lonhelptop.gif' /></a>
<h3>1. Constructing a query</h3>
<br clear='all' />
<p>
Queries are constructed with the three logical operators: AND, OR, and
NOT.  These logical operators combined with
search terms creates a logical expression (Boolean query).
Search terms can either be alphanumeric words, or phrases
delimited by quotation marks.  Logical operations can be
grouped together with parentheses.
</p>
<p>
Examples include:
</p>
<ul>
<li><tt>(Harrison and not Albertelli) or (Kortemeyer and "Alexander
Sakharuk")</tt></li>
<li><tt>not "invariant set" and topology</tt></li>
<li><tt>prokaryot or bacteria</tt></li>
<li><tt>not einstein and not bohr</tt></li>
</ul>
<p>
The search is case insensitive.  (Logical operators are also
evaluated in a case insensitive manner, e.g. and=AND.)
</p>
<br />&nbsp;<br />
<a name='scanningstatus' />
<a href='#helptop'>
<img border='0' align='left' src='/adm/lonIcons/lonhelptop.gif' /></a>
<h3>2. Understanding the Search Progress screen</h3>
<br clear='all' />
<p>
The Search Progress screen provides five pieces of
information.  This information is dynamically updated
every second as the search progresses across the
LON-CAPA network.
</p>
<ol>
<li>The number of library servers being scanned.</li>
<li>The number of database hits found.</li>
<li>The time elapsed (in seconds).</li>
<li>A grid showing the response status of every LON-CAPA library server.</li>
<li>A window for displaying response details of individual LON-CAPA
library servers.</li>
</ol>
<p>
The response status grid consists of the following symbols:
</p>
<ul>
<li><img src='/adm/lonIcons/srvnull.gif' />:
unknown; the server has yet to be contacted</li>
<li><img src='/adm/lonIcons/srvbad.gif' />:
a network connection cannot be established with
the server
</li>
<li><img src='/adm/lonIcons/srvhalf.gif' />:
a network connection was established to the
database, but search results have yet to be
completely transmitted from the database
</li>
<li><img src='/adm/lonIcons/srvempty.gif' />:
a network connection was established and all
search results are transmitted; however, there are no
matching records for this server for this search
</li>
<li><img src='/adm/lonIcons/srvgood.gif' />:
a network connection was established and all
search results are transmitted; there is at least
one matching record on this server for this search
</li>
</ul>
<br />&nbsp;<br />
<a name='outputview' />
<a href='#helptop'>
<img border='0' align='left' src='/adm/lonIcons/lonhelptop.gif' /></a>
<h3>3. Viewing the Output of Search Results</h3>
<br clear='all' />
<p>
The interface provides four different ways to format the output
of metadata information.
<ul>
<li><strong>Detailed Citation View</strong></li>
<ul>
<li><u>Description</u>:
Per database record, this view shows the following fields:
Owner, Last Revision Date, Title, Author, Subject, Keyword(s), Notes,
MIME Type, Language, Copyright/Distribution,
Extra custom metadata fields, and Short Abstract.
This view is meant to show a nicely formatted, detailed listing
of data describing a LON-CAPA resource.
</li>
<li><u>Example</u>:</li>
</ul>
<li><strong>Summary View</strong></li>
<ul>
<li><u>Description</u>:</li>
Per database record, this view shows the following fields:
Title, Owner, Last Revision Date, Copyright/Distribution, and
Extra custom metadata fields.
This view is meant to show a nicely formatted, condensed amount
of data describing a LON-CAPA resource.
<li><u>Example</u>:</li>
</ul>
<li><strong>Fielded Format</strong></li>
<ul>
<li><u>Description</u>:</li> This view shows all standard metadata fields
(as well as requested custom metadata fields) in the format of
<tt><b>field_name</b>: <b>field_value</b></tt>.
<li><u>Example</u>:</li>
</ul>
<li><strong>XML/SGML</strong></li>
<ul>
<li><u>Description</u>:</li>
This view shows all standard metadata fields
(as well as requested custom metadata fields) in the format of
<tt><b>&lt;field_name&gt;</b><b>field_value</b><b>&lt;/field_name&gt;</b></tt>.
<li><u>Example</u>:</li>
</ul>
</ul>
</p>
<br />&nbsp;<br />
<a name='controlwho' />
<a href='#helptop'>
<img border='0' align='left' src='/adm/lonIcons/lonhelptop.gif' /></a>
<h3>4. Controlling who can search through resources</h3>
<br clear='all' />
<p>
Currently, any user can see metadata for any published resource.
We are working to change this and are considering two possibilities:
</p>
<ol>
<li>
<pre>
Browsing and searching should only be
 
* either user specific (georgio can only browse and search
   /res/DOMAIN/georgio)
* or has advanced status as indicated by $env{'user.adv'}
</pre> 
</li>
<li>
<pre>
If user can access resource through current role (student in a
class, etc) then it should show up on searching and browsing.
Even if resource conditionals prevent actually viewing
the specific resource.  Advanced users can search and browse
"everywhere".
</pre>
</li>
</ol>
<br />&nbsp;<br />
<a name='engineperformance' />
<a href='#helptop'>
<img border='0' align='left' src='/adm/lonIcons/lonhelptop.gif' /></a>
<h3>5. Search engine performance measurements</h3>
<br clear='all' />
<p>
</p>
<br />&nbsp;<br />
<a name='softwarearchitecture' />
<a href='#helptop'>
<img border='0' align='left' src='/adm/lonIcons/lonhelptop.gif' /></a>
<h3>6. Notes on software architecture</h3>
<br clear='all' />
<p>
LON-CAPA is meant to distribute A LOT of educational content
to A LOT of people.  It is ineffective to directly rely on contents
within the ext2 filesystem to be speedily scanned for 
on-the-fly searches of content descriptions.  (Simply put,
it takes a cumbersome amount of time to open, read, analyze, and
close thousands of files.)
</p>
<p>
The solution is to hash-index various data fields that are
descriptive of the educational resources on a LON-CAPA server
machine.  Descriptive data fields are referred to as
"metadata".  The question then arises as to how this metadata
is handled in terms of the rest of the LON-CAPA network
without burdening client and daemon processes.  I now
answer this question in the format of Problem and Solution
below.
</p>
<p>
<pre>
PROBLEM SITUATION:

  If Server A wants data from Server B, Server A uses a lonc process to
  send a database command to a Server B lond process.
    lonc= loncapa client process    A-lonc= a lonc process on Server A
    lond= loncapa daemon process

                 database command
    A-lonc  --------TCP/IP----------------> B-lond

  The problem emerges that A-lonc and B-lond are kept waiting for the
  MySQL server to "do its stuff", or in other words, perform the conceivably
  sophisticated, data-intensive, time-sucking database transaction.  By tying
  up a lonc and lond process, this significantly cripples the capabilities
  of LON-CAPA servers. 

  While commercial databases have a variety of features that ATTEMPT to
  deal with this, freeware databases are still experimenting and exploring
  with different schemes with varying degrees of performance stability.

THE SOLUTION:

  A separate daemon process was created that B-lond works with to
  handle database requests.  This daemon process is called "lonsql".

  So,
                database command
  A-lonc  ---------TCP/IP-----------------> B-lond =====> B-lonsql
         <---------------------------------/                |
           "ok, I'll get back to you..."                    |
                                                            |
                                                            /
  A-lond  <-------------------------------  B-lonc   <======
           "Guess what? I have the result!"

  Of course, depending on success or failure, the messages may vary,
  but the principle remains the same where a separate pool of children
  processes (lonsql's) handle the MySQL database manipulations.
</pre>
</p>
<br />&nbsp;<br />
<a name='limitations' />
<a href='#helptop'>
<img border='0' align='left' src='/adm/lonIcons/lonhelptop.gif' /></a>
<h3>7. Limitations</h3>
<br clear='all' />
<p>
The metadata search can only consist of spaces and alphanumeric
characters.  Other characters are illegal and are filtered out
when sending the search request to the search engine.
</p>
<p>
LON-CAPA library servers are given 9 seconds to inform 
another server that they are in the process of generating
a reply to a search request.  Note that this is DIFFERENT
than actually conducting the search.  Upon initial communication,
the individual library servers just send a response key to
indicate the name of the results file that is going to be generated.
</p>
<p>
LON-CAPA library servers will only send up
to 100 records in response to a search.
</p>
<p>
The output of matching records is limited
to 200 records.
</p>
<p>
The capping of results to values of 100 and 200
should eventually be user modifiable.  These limitations
exist to avoid processing overly expansive search requests.
</p>
<br />&nbsp;<br />
</body>
</html>
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