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## -*- mode: html; coding: utf-8; -*-
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## Copyright (C) 2013 CERN.
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<!-- WebDoc-Page-Title: _(Search Services)_ -->
<!-- WebDoc-Page-Navtrail: <a class="navtrail" href="<CFG_SITE_URL>/help/hacking">Hacking Invenio</a> &gt; <a class="navtrail" href="search-engine-internals">WebSearch Internals</a> -->
<!-- WebDoc-Page-Revision: $Id$ -->
<h2>Contents</h2>
<strong>1. <a href="#1">Overview</a></strong><br />
<strong>2. <a href="#2">Enable/Disable a search service</a></strong><br />
<strong>3. <a href="#3">Build a custom search service</a></strong><br />
<strong>3.1 <a href="#3.1">Search service specifications/requirements</a></strong><br />
<strong>3.1.1 <a href="#3.1.1">3.1.1 Using SearchService base class</a></strong><br />
<strong>3.1.2 <a href="#3.1.2">3.1.2 Using ListLinksService class</a></strong><br />
<strong>3.1.3 <a href="#3.1.3">3.1.3 Using KnowledgeBaseService class</a></strong><br />
<strong>3.2 <a href="#3.2">Good practices</a></strong><br />
<a name="1"></a><h2>1. Overview</h2>
<p>Search services are meant to display information contextual to a
search query in very specialized way, in the sense that they can
search/retrieve/display data beyond the traditional concept of
records. Typical search services could for example include:
<ul>
<li>Spell-check user queries by calling an external spellchecking library, and offering "<em>Did you mean ...?</em>" options.</li>
<li>Parse user input and display an author profile when searching for a well-defined author.</li>
<li>Search for submission names matching the user input.</li>
<li>Retrieve phone number from the institutional LDAP.</li>
<li>Etc.</li>
</ul>
</p>
<p> Search services are displayed (in addition) just before the
results returned by the standard Invenio search engine. Each service
is queried with the context, and returns:
<ul>
<li>A score indicating the relevance of the response, given the context</li>
<li>An HTML formatted response</li>
</ul>
The relevance returned by the service is typically a score between 0
and 100 (see
<code>websearch_services.CFG_WEBSEARCH_SERVICE_MAX_SERVICE_ANSWER_RELEVANCE</code>
for details) which indicate how much the service <em>thinks</em> it
can address the "question" and how much it <em>thinks</em> it was able
to answer it. Given the wanted simplistic (non-scientific) nature of
services it is extremely important to consider the score very
carefully, and compare it with existing services when designing a new
service. Failing to do so might lead to hide more relevant answers
provided by other services with non-relevant information. </p>
<p> Services are designed to provide unobtrusive and useful
information to the user. To that end some measure are taken to cut
possible verbosity introduced by the services:
<ul>
<li>A maximum number of 2 (most relevant) services is displayed for each query. Defined in <code>websearch_services.CFG_WEBSEARCH_SERVICE_MAX_NB_SERVICE_DISPLAY</code>.</li>
<li>Service with a too low relevance (<21) are not displayed. Defined in <code>websearch_services.CFG_WEBSEARCH_SERVICE_MIN_RELEVANCE_TO_DISPLAY.</code></li>
<li>When the distance between the relevance of two services is too great (30), only the most relevant service out of the two is displayed. Defined in <code>websearch_services.CFG_WEBSEARCH_SERVICE_MIN_RELEVANCE_TO_DISPLAY.</code></li>
<li>When a service replies with too many answers, display only 4 answers of the services. More can be displayed when clicking "more".</li>
<li>Use a visually light theme.</li>
</ul>
See also the section <a href="#3.2">3.2 Good practices</a>.
</p>
<a name="2"></a><h2>2. Enable/Disable a search service</h2>
<p>In order to enable a service, drop its files into the following location: <br/>
<pre>
/opt/invenio/lib/python/invenio/search_services/
</pre>
</p>
<p>
To disable a service, remove the file from the above directory.
</p>
<a name="3"></a><h2>3. Build a custom search service</h2>
<p>Services use the Invenio <code>plugin_utils</code> infrastructure, and
are self-contained in single Pythonic files that comply with the
specifications defined in section <a href="#3.1">3.1 Search service
specifications/requirements</a>.</p>
<a name="3.1"></a><h2>3.1 Search service specifications/requirements</h2>
A search service is a Pythonic file stored
in <code>/opt/invenio/lib/python/invenio/search_services/</code>,
which name corresponds to a class defined in the file. <br/>
<p>In order to be valid, your service should inherit from the base
<code>SearchService</code> class and implement some functions (see
Section <a href="#3.1.1">3.1.1 Using SearchService base class</a>).
Other helper, more specialized classes exists to help you build
services that responds with links of links
(Section <a href="#3.1.2">3.1.2 Using ListLinksService class</a>) or
answer based on a BibKnowledge knowledge base (<a href="#3.1.3">3.1.3
Using KnowledgeBaseService class</a>)</p>
<a name="3.1.1"></a><h2>3.1.1 Using SearchService base class</h2>
<p>Start implementing your service by defining a class that inherits from
the <code>SearchService</code> base class. Choose a class name that
matches the name of your service file.
</p>
<p>
For eg. a spellchecker service could exist
in <code>/opt/invenio/lib/python/invenio/search_services/SpellCheckerService.py</code>,
with the following content:
<pre style="border:1px solid #bbb; overflow-x:auto;padding:5px;">
from invenio.websearch_services import SearchService
__plugin_version__ = "Search Service Plugin API 1.0"
class CollectionNameSearchService(SearchService):
def get_description(self, ln=CFG_SITE_LANG):
"Return service description"
return "Spell check user input"
def answer(self, req, user_info, of, cc, colls_to_search, p, f, search_units, ln):
"""
Answer question given by context.
Return (relevance, html_string) where relevance is integer
from 0 to 100 indicating how relevant to the question the
answer is (see C{CFG_WEBSEARCH_SERVICE_MAX_SERVICE_ANSWER_RELEVANCE} for details) ,
and html_string being a formatted answer.
"""
[...]
return (score, html_answer)
</pre>
</p>
<p>The bare minimum for a search service to be valid is to inherit from
the abstract base class "<code>SearchService</code>". The service
must:<br/>
<ul>
<li>Override <code>get_description(..)</code> to return a short description of the service.</li>
<li>Override <code>answer(..)</code> to return an answer (int, html_string).</li>
<li>Define <code>__plugin_version__</code> for the Search Service plugin version this service is compatible with.</li>
</ul>
</p>
<p>If your service must pre-process some data and cache it, it can
override the following helper methods:
<ul>
<li> <code>prepare_data_cache(..)</code> to prepare some cache needed
to answer. The returned structure is cached for you and can be
retrieved later via the <code>self.get_data_cache()</code>
function. This method is called only when the service is queried and
the cache has not yet been prepared, or must be refreshed. The
Invenio <code>DataCacher</code> infrastructure is used, to store the
cache in memory.</li>
<li><code>timestamp_verifier(..)</code> to indicate if cache
must be refreshed, by returning the latest modification timestamp of
your data.</li>
</ul>
</p>
<a name="3.1.2"></a><h2>3.1.2 Using ListLinksService class</h2>
<p>If your service is designed to display list of responses, you can
inherit from the <code>ListLinksService</code> class instead
of <code>SearchService</code>, in order to benefit from the following
additional helper functions:
<pre style="border:1px solid #bbb; overflow-x:auto;padding:5px;">
from invenio.websearch_services import ListLinksService
from invenio.messages import gettext_set_language
__plugin_version__ = "Search Service Plugin API 1.0"
class CollectionNameSearchService(ListLinksService):
[...]
def get_description(self, ln=CFG_SITE_LANG):
"Return service description"
return "A foo that answer with list of bars"
def get_label(self, ln=CFG_SITE_LANG):
"""
Return label displayed next to the service responses.
@rtype: string
"""
_ = gettext_set_language(ln)
return _("You might be interested in")
def answer(self, req, user_info, of, cc, colls_to_search, p, f, search_units, ln):
"""
Answer question given by context.
Return (relevance, html_string) where relevance is integer
from 0 to 100 indicating how relevant to the question the
answer is (see C{CFG_WEBSEARCH_SERVICE_MAX_SERVICE_ANSWER_RELEVANCE} for details) ,
and html_string being a formatted answer.
"""
[...]
return (score, self.display_answer_helper(list_of_tuples_labels_urls))
</pre>
<ul>
<li><code>get_label(..)</code> to return the label displayed to the
user for the service next to the list of responses.</li>
<li><code>display_answer_helper(..)</code> a function to be used as
a help to process a list of tuples (label, url) in order to return
a nicely formatted list of items from the <code>answer().</code>
function</li>
</ul>
</p>
<p>The requirements from the base class <code>SearchService</code> are
still valid when using <code>ListLinksService</code>:
<ul>
<li>Override <code>get_description(..)</code> to return a short description of the service.</li>
<li>Override <code>answer(..)</code> to return an answer (int, html_string).</li>
<li>Define <code>__plugin_version__</code> for the Search Service plugin version this service is compatible with.</li>
</ul>
</p>
<a name="3.1.2"></a><h2>3.1.3 Using KnowledgeBaseService class</h2>
<p>
If you would like to build a service that answers automatically based
on the values stored in a BibKnowledge knowledge base, use
the <code>KnowledgeBaseService</code>. In this case you do not need to
define the <code>answer(..)</code> function, which is already
implemented for you:
</p>
<pre style="border:1px solid #bbb; overflow-x:auto;padding:5px;">
from invenio.websearch_services import KnowledgeBaseService
from invenio.messages import gettext_set_language
__plugin_version__ = "Search Service Plugin API 1.0"
class MyKBService(KnowledgeBaseService):
[...]
def get_description(self, ln=CFG_SITE_LANG):
"Return service description"
return "A foo that answer with list of bars, based on myKB"
def get_label(self, ln=CFG_SITE_LANG):
"""
Return label displayed next to the service responses.
@rtype: string
"""
_ = gettext_set_language(ln)
return _("You might be interested in")
def get_kbname(self):
"Load knowledge base with this name"
return "myKB"
</pre>
<p>With the above code, the knowledge base "<em>myKB</em>" will be
loaded and used to reply to the user. It is expected that the
knowledge base contains for each mapping a list of
whitespace-separated as key, and a label + url (separated with a "|")
as value. For eg:
<pre style="border:1px solid #bbb; overflow-x:auto;padding:5px;">
help submit thesis -> How to submit a thesis|http://localhost/help/how-to-submit-thesis
Atlantis Times -> Atlantis Times journal|http://localhost/journal/AtlantisTimes
</pre>
</p>
<p>When filling up the knowledge base keys, one should carefully
select the keywords in order to focus on a very specific subject, and
avoid too generic terms that would unnecessarily match too many user
queries. One should also consider the possible clash with other
services (the first rule of the above KB example might for example
hide responses from the "<em>SubmissionNameSearchService</em>"
service </p>
<p>
A default implementation of a <code>KnowledgeBaseService</code> is
provided with Invenio: "<em>FAQKBService</em>". This service makes
use of the demo knowledge base named "FAQ".
</p>
<a name="3.2"></a><h2>3.2 Good practices</h2>
<ul>
<li>Gradually try to understand if the service can answer the question,
and exclude it as quickly as possible (avoid heavy computation if
the service is not concerned by the question).</li>
<li>It would often make sense to exclude the service if a user is
querying using search field (for eg. author field).</li>
<li>Avoid noise and redundancy by providing only services that you
think will be useful to your users, or make sure that they mutually
exclude each other in the area they cover.</li>
<li>Be cautious when returning a relevance score, in order to ensure
that your service will not hide other that might be more
relevant. Test and consider other services. Follow the guidelines
regarding the score to return.</li>
<li>Avoid matching too generic terms and stop-words, such as
"document", "the", "to", etc. Be careful when using some keyword such
as "how", "search", etc.</li>
</ul>
<p>See also <a href="#1">1. Overview</a> section.</p>

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