ZCatalog Tutorial

  This document provides a tutorial for 'ZCatalog', the new search
  engine machinery in Zope.  The audience for the document is content
  managers.

  Contents

    o What is it?  What's it for?  Why's it so cool?

    o Installing ZCatalog

    o ZCatalog Objects

    o Example using ZCatalog

    o Creating Search Forms And Result Reports

    o Using ZCatalog In A Zope Site

    o ZCatalog vs. Catalog

  What is it?  What's it for?  Why's it so cool?

    The 'ZCatalog' provides powerful indexing and searching on a Zope
    database using a Zope management interface.  A 'ZCatalog' is a
    Zope object that can be added to a Folder, managed through the
    web, and extended in many ways.

    The 'ZCatalog' is a very significant project, providing a number
    of compelling features:

      o **Searches are fast**.  The data structures used by the index
      provide extremely quick searches without consuming much memory.

      o **Searches are robust**.  The 'ZCatalog' supports boolean
      search terms, proximity searches, synonyms and stopwords.

      o **Indexing is wildly flexible**.  A 'ZCatalog' can catalog
      custom properties and track unique values.  Since 'ZCatalog'
      catalogs objects instead of file handles, you can index any
      content that can have a Python object wrapped around it.  This
      also lets objects participate in how they are cataloged,
      e.g. de-HTML-ifying contents or extracting PDF properties.

      o **Usable outside of Zope**.  The software is broken into a
      Python 'Catalog' which wrapped by a 'ZCatalog'.  The Python
      'Catalog' can be used in any Python program; all it requires is
      the Z object database and the indexing machinery from Zope.

      o **Transactional**.  An indexing operation is part of a Zope
      transaction.  If something goes wrong after content is indexed,
      the index is restored to its previous condition.  This also means
      that Undo will restore an index to its previous condition.
      Finally, a 'ZCatalog' can be altered privately in a Version,
      meaning no one else can see the changes to the index.

      o **Cache-friendly**.  The index is internally broken into
      different "buckets", with each bucket being a separate Zope
      database object.  Thus, only the part of the index that is needed
      is loaded into memory.  Alternatively, an un-needed part of the
      index can be removed from memory.

      o **Results are lazy**.  A search that returns a tremendous
      number of matches won't return a large result set.  Only the
      part of the results, such as the second batch of twenty, are
      returned.

    The 'ZCatalog' is a free, Open Source part of the Zope software
    repository and thus is covered under the same license as Zope.  It
    is being developed in conjunction with the Zope Portal Toolkit
    effort.  However, the 'ZCatalog' product is managed as its own
    module in CVS.

  Installing ZCatalog

    'ZCatalog' can be downloaded from the Zope download area and is
    also a module in the public CVS for Zope.  Untar it while in the
    root directory of your Zope installation::

      $ cd Zope-2.0.0a3-src/
      $ tar xzf ../ZCatalog-x.x.tgz

    Windows users can use WinZip or a similar utility to accomplish
    the same thing.

    Also, Zope 2.0.0a3 does not have the latest version of UnIndex and
    UnTextIndex which fix a couple of bugs in the alpha 3 versions.
    The latest CVS of the SearchIndex packages *must* be used.

    Remember, you have to restart your Zope server before you will see
    'ZCatalog'.

  ZCatalog Objects

    A 'ZCatalog' performs two activities: indexing information and
    performing searches.

    Most the work is done in the first step, which is getting objects
    into the index.  This is done in two ways.  First, if your objects
    are ZCatalog-aware they automatically update the index when they
    are added, edited or directly deleted.  A ZCatalog-aware object is
    one that is an instance of a 'Z Class' that informs the 'ZCatalog'
    of changes.  *Directly deleted* means the object was deleted from
    a Folder, not the deletion of a containing Folder.

    The second way that site contents get updated is by "finding"
    information "into" the 'ZCatalog'.  An operation based on Zope's
    Find view traverses Folders looking for objects matching the
    criterion.  The objects are then registered with the Catalog.
    Objects in the index but no longer in the site are removed from
    the Catalog.

    Either way -- automatically updating or walking the Folders --
    'ZCatalog' indexes the objects it finds.  The 'ZCatalog' is set up
    to look for properties, each of which are added to the index.

    There are two kinds of indexes, called FieldIndex and TextIndex.
    FieldIndex indexes treat data atomically.  The entire contents of a
    FieldIndex-indexed property is treated as a unit.  With a
    TextIndex index, it is broken into words which are indexed
    individually.  A TextIndex is also known as *full-text index*.

    Note that the 'ZCatalog' doesn't track ZCatalog-unaware objects
    after it has indexed them.  This means that the 'ZCatalog' must
    reindex its objects occasionally when the objects have been
    changed.  Out of date indexes can be prevented by inheriting from
    a ZCatalog-aware class which can tell the 'ZCatalog' to reindex it
    whenever a change is made.  Just such a class will be included
    with the Portal toolkit.

    ZCatalogs are "searchable objects", meaning they cooperate with Z
    Search Interfaces documented in Z SQL Methods.  Creating a search
    form for a 'ZCatalog' is a simple matter of adding a Z Search
    Interface from the management screen and filling in a form.
    ZCatalogs can also be queried directly from DTML, as shown in the
    example below.

  Example using Z Classes

    The first example shows how to give your Zope site a long-desired
    feature: full text-searches of your content.  The example assumes
    you already have a number of DTML Methods/Documents to catalog.

        o Install 'ZCatalog' as instructed above

        o In the root folder of your Zope server, add a 'ZCatalog'.

        o Type in the id 'catalog' and hit 'Add'.

    You now have a brand new 'ZCatalog' named 'catalog' in your root
    folder.

        o Click on it.

    Now you are looking at the 'ZCatalog' 'Contents' view.  It says
    the catalog is empty.  We'll catalog some objects in a moment, but
    first we have to tell it what portions of objects we are
    specifically interested in.

        o Click on 'Indexes'.

    This management view is where the attributes to be indexed are
    defined.

        o In the 'Add index' field, type 'raw'.

        o Click 'Add'.

    Now that the indexes are defined, a set of objects can be selected
    for cataloging.
    
        o Click on 'Find items to ZCatalog'.

    For this example, we are only interested in DTML Documents and
    Methods.

        o Deselect 'All type'.

        o Select 'DTML Method' and 'DTML Document'.

        o Click 'Find'.

    ZCatalog will report how many items it found, and then present an
    interface for excluding specific objects.
    
        o Click 'Catalog Items'.

    Great, now that the catalog is stocked, we can create a user
    interface to it.
    
        o Return to the root folder's management view.

        o Add a 'Z Search Interface'.

    'ZCatalog' participates in the Zope Search architecture.  You
    simply have to fill in this form, and a basic user interface will
    be created.

        o Select 'catalog' in the list beside 'Select one or more searchable
          objects'.
        
        o Beside 'Report Id', type 'report'.

        o Beside 'Search Input Id', type 'search'.

    'report' and 'search' are the Ids of two DTML Methods which will
    be created in your root folder.

        o Click 'Add'.

    Congratulations, if all has gone well, you can now find references
    to any word in your DTML pages.  Try it by viewing 'search'.  Type
    a common word in the 'Raw' field, and you should be presented with
    a list of hits.  However, none of the results returned can be
    clicked on.  To fix this, go to the management view of 'report'.
    'report' is called by 'search' to display the results from
    'catalog'.  'report' is just a simple '<!--#in catalog-->' loop
    with a few refinements.  'catalog' knows which results to return
    by looking at the REQUEST variable, which contains the input from
    the 'search' form.

        o In the source of 'report', find the following line::

            <tr><!--#var title--></tr>
        
        o Replace it with this::

            <tr>
             <a href="<!--#var "catalog.getpath(data_record_id_)"-->">
              <!--#var title-->
             </a>
            </tr>

    This is a little confusing at first.  Keep in mind that ZCatalog
    does not return a list of your database objects.  What it returns
    are actually fairly unintelligent instances of a Record subclass.
    These record objects contain copies of data from attributes of
    catalog objects.  The 'ZCatalog' 'MetaData Table' view defines
    which attributes are copied.

    (By default, these record objects are just SLIGHTLY more
    intelligent than a raw tuple.  'Catalog' can be told to use a
    custom, intelligent class for results.  Please see the 'Catalog'
    __init__ method in 'lib/python/Products/ZCatalog/Catalog.py' for
    more information.)

    Fortunately, ZCatalog provides a utility function for going from
    result objects to the object's path.  It is called, aptly enough,
    'getpath'.  'getpath' expects to be passed the unique integer
    identifier of the cataloged object.  Results store that id as
    'data_record_id_'.

    Commit this change, and perform another search.  Now the title can
    be clicked on to take you to the full page.
    
  Example cataloging custom objects

    As if full-text searches of your entire site weren't good enough,
    ZCatalog can also catalog Z Classes, Products, and in fact any
    Python object you can put in a ZODB.  Here is an example using a Z
    Class, but the principles apply to any kind of object.

    First, we're going to need something to catalog.  Follow the 'Z
    Class' tutorial to create the CD 'Z Class'.  Back?  Good.

        o Create a folder, 'CDs', and create a number of instances of
        the CD Z Class in it.

    'cd1' through 'cd5' should be plenty.  Remember to fill each of
    them in from their Properties view.

    Now we want to create a searchable catalog of CDs.

      o Go to the 'CDs' folder and create a 'ZCatalog' with an ID 'cd_cat'.

      o Click on the objects Indexes view.

    This screen shows that, by default, 'ZCatalog' is interested in an
    object's 'id','title', 'meta_type', and
    'bobobase_modification_time'.  You will almost always want to
    index additional information.  In this case, we would also like to
    index the artist and description of CDs.

      o Type 'artist' into the 'Add Index' field. 

    For the sake of example, we're going to use a FieldIndex index for
    artist.  This will give us the option of putting an HTML SELECT
    box for artists on the search form.

      o Select FieldIndex from the Index type drop down, and click
      'Add'.

      o Also add an index for 'description', but leave TextIndex
      selected.

    This will allow us to search for individual words within the
    description.

      o Click on 'MetaData Table'.

    This is where we tell the 'ZCatalog' what attributes of cataloged
    objects to cache.  These cached values are available from search
    results without having to look up the actual indexed object.  The
    tradeoff for the speed is extra memory, as information from the
    content is duplicated in the 'ZCatalog'.

    You will probably want to keep the schema light-weight, so we're
    not going to add 'description' to it.  Type 'artist' in the 'Add
    column' field and click 'Add'.

      o Click on the 'Find Items to Catalog' view.

    This is the interface you use to tell the 'ZCatalog' which items
    to index.  Right now, beside 'Find objects of type:', 'All types'
    is selected.

      o Deselect 'All types'.

      O Scroll down and select CD.

    You could use the rest of the form to be more specific, but since
    we want to catalog all the CDs,

      o Click 'Find'.

    'ZCatalog' will report 'Found 5 items.'  It is now giving you an
    opportunity to exclude some of the matched items from the index.
    Again, we want all of them, so,

      o Click 'Catalog Items'.

    You should at this point see a list of the indexed objects.  Also
    of note is the 'Update Catalog' button.  You have to use it
    whenever you want your 'ZCatalog' to notice changes you've made to
    the objects it's indexed.

  Creating Search Forms And Result Reports

    This catalog isn't much good without some way of querying it.

      o Go back to your 'CDs' folder's management screen and add a Z
        Search Interface.

    The search add form will automatically detect your cd_cat
    'ZCatalog' and offer it as a searchable document.  Make sure it is
    selected.

      o Fill in 'cd_report' for 'Report ID' and 'cd_search' for
        'Search Input ID'.

    Those are the ids of two DTML methods that will be generated in
    the 'CDs' folder.

      o Click 'Add'.

      o View the 'cd_search' Catalog (at, for example,
        http://localhost:9673/CDs/cd_search).

    You will see a basic search interface, with fields for searching
    on 'title', modification date, 'id', 'artist', 'meta type' and
    'description'.  If you fill in one more more of the fields and
    click 'Submit Query', cd_report will be displayed.  It is passed
    the search criteria and uses it to get a list from cd_cat to
    iterate over.  It is merely displaying the information from the
    ZCatalog's MetaData table, but of course it can be enriched.

    Try a few more searches.  You'll find that you can type any single
    word from the title or description and get a match, but for artist
    you must type the exact string.  That's because artist was indexed
    as a FieldIndex, which gives us an opportunity to present a more
    convenient interface.

    Go back to the 'cd_search' management interface, and change
    it's source to look like this::


  Enter query parameters:

   Title
       
   Artist
              
        All

   Description

    This is a search form somewhat more appropriate for the CD 'Z
    Class'.  Unrelated fields have been removed, and the 'artist'
    field has been changed to a drop-down menu.  Let's augment the
    output of 'cd_report' to make the title a link to the actual CD
    object.

    Taking a look at 'cd_report', note that the search results are
    obtained with a simple '<!--#in cd_cat ...-->' tag.  The search
    criteria is automatically obtained by the 'ZCatalog' from the form
    input.  The line we're interested in is this one::

            <td><!--#var title--></td>

    Change it to read::

            <td>
             <a href="<!--#var "cd_cat.getpath(data_record_id_)"-->">
              <!--#var title-->
             </a>
            </td>

    Now, assuming you have added the index_html document template to
    your CD 'Z Class', clicking on a search result will take you to
    the CD's detailed display.

  Using 'ZCatalog' In A Zope Site

    The 'ZCatalog' provides high-speed access to what is on your site.
    Thus, the 'ZCatalog' can be used to re-engineer the way your site
    is laid out.

    For instance, a Slashdot-style presentation is simple.  Just
    insert some DTML that asks the 'ZCatalog' for recent items.
    Alternatively, a Site Map is nothing more than presenting the
    contents of the catalog.  A page with tree-based browsing of
    software packages by category is also easy.  Perhaps you'd like to
    provide a link that lists all the packages the current user has
    authored.

    Thus, the 'ZCatalog' isn't just about searching.  It can be used
    as the DTML-scriptable engine for browsing a site as well.

    Since the 'ZCatalog' is a normal Zope folderish object, you can
    also create DTML Methods inside it to present the catalog
    contents.  For instance, perhaps you'd like to dump the contents
    of the site as an RDF stream, or do content syndication with RSS.
    These are just DTML Methods that change the 'Content-Type:' and
    send back XML.  All without actually waking up any of the content
    objects in the site.

  ZCatalog vs. Catalog

    The real star of this package is the 'Catalog' module.  All the
    heavy lifting is done by 'Catalog'.  'ZCatalog' is basically a
    Zope-aware wrapper around Catalog, which can be used on it's own
    outside the Zope framework.  The only requirement is that you are
    using ZODB as your object store.
