In a SharePoint environment, users can perform searches from team sites hosted
by Windows SharePoint Services and from portal sites hosted by Microsoft Office
SharePoint Portal Server 2003. (For definitions of team sites, portal sites,
and other types of sites, see the sidebar "Types of SharePoint Sites.") SharePoint
Services and Portal Server use the same search engine, but the different ways
they use that engine result in an inconsistent search experience for end users.
Learning about the two products' different search architectures can help you decide whether your users would benefit most by using SharePoint Services, Portal Server, or both together. If you haven't yet deployed SharePoint, understanding SharePoint search architecture will help you plan for an eventual deployment.
Major Search Components
Microsoft Search Service (MSSearch) is the generic search service that Microsoft
products, including SharePoint Services and Portal Server, use to varying degrees.
It supports three query languages—Query Dialect 1, SQL full-text extensions,
and Query Dialect 2—which let users perform varied forms of queries. MSSearch
creates full-text indexes on content and properties of structured and semistructured
data and allows fast linguistic searches on this data.
For an index to be truly useful, however, it must support the content sources that users are interested in (e.g., file shares, Web content, Exchange Server folders, SharePoint-based sites) and the types of data within those content sources, and it must offer rich retrieval capabilities. The applications that use the index need to provide the content to be indexed, format user queries, and return the results of searches to the requesting clients. Consequently, these applications in effect control the overall search experience, and some exercise that control much better than others. Portal Server, for example, provides content to be indexed from many sources, such as Exchange public folders and IBM Lotus Notes databases, whereas SQL Server full-text indexing provides content only from SQL Server tables.
MSSearch relies on several major components to support full-text indexing.
Figure 1 shows the following components:
- Protocol handlers—access data over a particular protocol or from a
particular store. Common protocol handlers can access data from file shares,
Web sites, public folders, Lotus Notes, and SQL Server databases. The protocol
handler processes URLs passed to it by the gatherer.
- Gatherer—maintains the queue of URLs to be accessed across protocols.
For each document accessed, the gatherer fetches the stream of content from
the protocol handler and passes it to the appropriate filter.
- Filters, also known as IFilters—extract textual information from
a specific document format and pass strings of text and property/value pairs
to the indexing engine. For example, the Microsoft Office IFilter extracts
terms from Microsoft Word, Excel, and PowerPoint files. Other IFilters work
with HTML or email messages. Third-party providers offer other specialized
filters; for example, Adobe Systems provides a PDF IFilter. Without an IFilter,
the text within the file can't be indexed.
- Word breakers and stemmers—word breakers determine where the word
boundaries are in the stream of characters in the query or the document being
crawled and break up compound words and phrases for the full-text index. A
stemmer extracts the root form of a given word. In some languages, the stemmer
expands the root form of a word to alternative forms—for example, providing
running, ran, and runner from the root word run .
- Indexer—prepares an inverted index of content. An inverted index is
a data structure with a row for each term. Each row contains information about
the documents in which the term appears and the number of occurrences and
relative position of the term within each document. The inverted index provides
MSSearch with the ability to apply statistical and probabilistic formulas
to quickly compute the relevance of documents.
- Alerts—notify users when new or updated content matches any queries
they've stored, as well as when changes have been made to documents, sites,
lists, and libraries.
- AutoCat—provides a way for items in a portal site to be automatically
cataloged with existing items in other areas. AutoCat uses a Topic Assistant,
which suggests alternative locations where items could logically be added
to lists or document libraries.
- Catalogs—store full-text indexes within the file system on the server
that runs the MSSearch service. Applications interact with MSSearch to maintain
the indexes and the catalogs.
Individual products also contribute to MSSearch's search architecture. For example, Portal Server adds Alerts to the search architecture, and third parties can provide filters and protocol handlers. However, not all products benefit from all of MSSearch's search components. For example, only Portal Server uses Alerts, but any product that uses the MSSearch architecture will benefit from IFilters.
Now that we understand a little about the search architecture, let's see how
SharePoint Services and Portal Server differ in the way they use the architecture.
We'll also look at how this difference results in different outcomes for end
users searching SharePoint sites.
Searching with SharePoint Services
SharePoint Services relies on SQL Server full-text indexing, which in turn interacts
with MSSearch. Thus, the search capabilities that SharePoint Services can offer
to team sites are limited by what SQL Server full-text indexing can do. One
prerequisite for enabling search within a team site is that SharePoint Services
must use SQL Server rather than Windows MSDE (WMSDE) as its storage engine.
By default, full-text indexing is disabled, but you can enable it by using the
SharePoint Central Administration page. No search links will appear on team
sites unless you enable full-text indexing.
SQL Server full-text indexing provides a protocol handler for MSSearch that understands only the content of SQL Server databases and tables. Therefore, the results of a search initiated from a team site include content only from SQL Server. When you enable searching in SharePoint Services, you enable it for all team sites because content from different team sites isn't separated into different tables. For example, the Docs table in a content database contains documents stored in all libraries within all team sites that use that content database.
A search from a team site supports stemming and inflectional forms (i.e., different
forms of a word) of the supplied query terms. In SharePoint Services, you're
limited to using exceptionally basic search terms, and neither phrase nor Boolean
searches are supported. Additionally, you can't narrow a search to within a
previous result set, and you won't see any indication of the number of hits.
Although you can limit a search's scope to the contents of an individual list,
the search is performed against the current view of that list and won't return
results for items that are filtered out of that view.
SharePoint Services' search capabilities are fairly inflexible and not designed for enterprise use. SharePoint Services indexes document content only, not any properties that might further describe the document's contents. Even if the search engine did index document properties, the query interface doesn't support advanced search, so users wouldn't find that information. Users are limited to doing a full-text search on content only. Furthermore, SharePoint Services' search capabilities are limited in scale, severely restricting their use in large server farms, which could conceivably contain millions of documents across thousands of team sites.
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