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FOA versus database retrieval

Within the field of computer science, the subfields of databases and IR are often closely aligned. Databases have well-developed theoretic underpinnings [Vianu97] that has generated efficient algorithms [McFadden94] and become the foundation for one of the most successful elements of the computer industry.

Both databases and search engines attempt to characterize a particular class of queries by which many users are expected to attempt to get information from computers. Historically, database systems and theory have been perceived as central to the discipline of Computer Science, probably more so than the IR techniques that are the core technologies for FOA. How many computer science departments in the US offer undergraduate classes in Databases? In IR? How many graduate classes? How many journals or conference proceedings, associated with the ACM or IEEE, are published in each area? Things may be changing, however.

The general public's discovery of the Internet and subsequent interest in search engines like Alta Vista, InfoSeek and Yahoo! suggests that many users find value in the lists of the Web pages returned in response. These search engines are clearly doing an important job for many people, and it is a different job than they use to organize their address book (record collection, baseball statistics, ...) {databases}. How are IR and database technologies to be distinguished?

To make the distinctions more concrete, let's imagine a particular information need and think about how both a database and a search engine might attempt to satisfy it. An example query might be:

What is the best SCSI disk drive to buy?

In the case of databases, strong assumptions must first be made about {structure} among attributes of individual records. Good database design demands that the fundamental elements of data, their format, and logical relations among them be carefully analyzed and anticipated in a LOGICAL DATA MODEL long before any data is actually collected and maintained within some physical implementation. These assumptions allow specification of a syntax for the query language, strategies for optimizing the query's use of computational resources, and efficient storage of the data on physical devices.

Let's now assume that a logical data model like this has been constructed and that a large catalog of information from various hard drive manufacturers and vendors has been collated. We will also make the much larger and problematic assumption that the users are capable of translating the natural language of Q1.3 into the somewhat baroque syntax of a query language like SQL. The result of the database search might look something like:

Creating an example relation like this and populating it with a few instances is simple, but performing the necessary data modeling, collating the data from all of the various manufacturers and vendors, and keeping it all up to date is a much more daunting task. If the database catalog is out of date, or missing data from some important vendors, users might well leave the database badly informed.

Now let's imagine using a search engine on the same query. When run against a Usenet news search engine like DejaNews, this query results in the retrieval shown in Figure (figure) with the most highly ranked posting shown in Figure (FOAref)

On Thu, 28 Aug 1997 23:10:03 GMT, Michael Query wrote:

>My question is, should I get another 2 Gb SCSI disk for putting the >OS (NT 4.0 WS), software, etc on, or should I get an IDE disk for this?

Having played around with different configs for a while, I'd say go SCSI. I'd do that even if I had to get a second SCSI controller.

(You'll ``hear'' a lot of people arguing that IDE is good enough, but if you are after overall improved performance SCSI is best.)

my 2Y. \caption{One posting retrieved}

Users of this search engine will read about many issues {\em related} to hard disks, some of which may be {\em relevant} to their particular situation. For example, does the ``best'' qualifier in Q1.3 mean lowest cost, maximum capacity, minimum access time,...? Are users able to choose between IDE and SCSI, or restricted to SCSI? Depending upon just what kind of users they are, some of the information retrieved may be immediately applicable to the purchase being considered, while other parts of it are better considered COLLATERAL KNOWLEDGE (D. E. Rose, personal communication) that simply leaves users more well-educated.

A very different set of assumptions are necessary to imagine the search engine working than those we made about the database system above. For example, just who wrote these postings? Are they a credible source of good information; what is their AUTHORITY ? The well-trained database users should ask equally skeptical questions about the data retrieved, but rarely are authority, data integrity, etc. considered really part of database analysis.

But the key assumption for our IR users are that they can ``listen in'' on this previous ``conversation'' and {interpret} the text that has been left behind as containing potential answers to his or her current question. The search engine is charged with retrieving textual passages that are at least likely to answer the users' questions. Once presented with these retrievals, the FOA users have more humble expectations, and are willing to do more interpretive work. Because FOA searches are often even less concrete than this query, issued by users simply trying to learn about a topic, {\em semantic} issues central to the interpretation of a textual passage and its context, validity, etc. are at the heart of the FOA enterprise.

has summarized these issues along a number of dimensions by which IR and database systems can be distinguished, and several of these are duplicated in Table (FOAref) :

Database systems are almost always assumed to provide data items directly. Search engines provide a level of indirection, a { pointer} to textual passages which contain many facts, hopefully including some of interest. The information need of the users is quite vague when compared to that of the database users. The search engine users are searching for information about a topic they understand incompletely. Typical database users have a fairly specific question, like Q1.3 above, in mind. It might even be that the database is missing some data; for example the special null value \O\ shows that the price of the third disk drive in Figure (FOAref) is not known. Even in this case, however, the database system ``knows that it doesn't know'' this fact. FOA queries are rarely brought to such a sharp point; ambiguity is intrinsic to the users' expectations.

Because the queries are so general, an FOA retrieval must be described in probabilistic terms. If a particular hard disk's price is part of our database, we are certain, with probability=1.0, of its value. Never would a database system reply with ``This hard disk might cost about As discussed in depth in Section §5.5 , a search engine can employ sophisticated methods for reasoning probabilistically, and available evidence might even allow it to be quite confident that retrieved items will be perceived as relevant. But never will we be entirely certain that a document will be what users want, only that we have high confidence it may be.

Finally, one of the problems in evaluating search engines is just what success criteria are to be used. In a database system we typically assume that what we get back from the database system is correct. (Try to find an ad for a database system that boasts, ``Our system retrieves only right answers''!) Database systems are claimed to be more efficient, cheaper, easier to integrate into existing code, more user-friendly.

This list of ways search engines might be distinguished from databases is far from exhaustive; Blair has proposed a more extensive analysis [Blair84] . More recently, as search engine technology and WWW-inspired applications have both burgeoned, hybrids of database and search have blurred the historical differences further. Some bases of database/search engine interaction are mentioned in Chapter §6 .

Chapter §4 discusses the evaluation of search engines in great detail, but typically the bottom line is - Does the system help you? If you are writing a research paper, did this search engine help you find materials that were useful in your search? If you are a lawyer preparing a case, and you want to find every relevant judicial opinion, does the search engine offer an advantage over an equavalent amount of time combing through the books in a law library? Such squishy, qualitative judgements are notoriously difficult to measure, and especially to measure consistently across broad populations of users. The next section provides a quick preview of several precise measurements that have proven useful to the IR community, but would not be found persuasive within the database community.


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