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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 the
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 atomicly. 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
chanced. 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 them each
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::
<xmp>
<!--#var standard_html_header-->
<form action="cd_report" method="get">
<h2><!--#var document_title--></h2>
Enter query parameters:<br><table>
<tr><th>Title</th>
<td><input name="title"
width=30 value=""></td></tr>
<tr><th>Artist</th>
<td>
<select name="artist">
<option value="">All</option>
<!--#in expr="cd_cat.uniqueValuesFor('artist')"-->
<option value="<!--#var sequence-item-->">
<!--#var sequence-item-->
</option>
<!--#/in-->
</select>
</td>
</tr>
<tr><th>Description</th>
<td><input name="description"
width=30 value=""></td></tr>
<tr><td colspan=2 align=center>
<input type="SUBMIT" name="SUBMIT" value="Submit Query">
</td></tr>
</table>
</form>
<!--#var standard_html_footer-->
</xmp>
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.
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