Automated Product Matching, Part I: Challenges

Bazaarvoice’s flagship product is a platform for our clients to accept, display and manage consumer generated content (CGC) on their web sites. CGC includes reviews, ratings, images, videos, social network content, etc. Over the last few years, syndicating CGC from one site to another has become increasingly important to our customers. When a user submits a television review on Samsung’s branded web site, it benefits Samsung, Target and the consumer when that review can be shown on Target’s retail web site.

Before syndicating CGC became important to Bazaarvoice, our content could be isolated for each individual client. There was never any need for us to consider the question of whether our clients had any overlap in their product catalogs. With syndication, it is now vital for us to be able to match products across all our clients’ catalogs.

The product matching problem is not unique to Bazaarvoice. Shopping comparison engines, travel aggregators and ticket brokers are among the other domains that require comprehensive and scalable automated matching. This is a common enough problem that there are even a number of companies trying to grow a business based on providing product matching as a service.


I have helped design and build product matching systems five different times across two different domains and will share some of what I have learned about the characteristics of the problem and its solutions. This article will not be about specific algorithms or technologies, but guidelines and requirements that are needed when considering how to design a technical solution. This will address not just the algorithmic challenges, but also the equally important issues with designing product matching as a system.

Blog posts are best kept to a modest length, and I have many more thoughts to share on this topic than would be polite to include in a single article, so I have divided this discussion into two parts. This blog post is about the characteristics that make this an interesting and challenging problem. The second posting will focus on guidelines to follow when designing a product matching system.

The focus here will be on retail product matching, since that is where my direct experience lies. I am sure that there are additional lessons to be learned in other domains, but I think many of these insights may be more broadly applicable.

“If at first you don’t succeed, you must be a programmer.”

Imprecise Requirements

Product matching is one of those problems that initially seems straightforward, but whose complexity is revealed only after having immersed oneself in it. Even the most enlightened product manager is not going to have the time to spell out, in detail, how to deal with every nuance that arises. Understanding problems in depth, and filling in the large numbers of unspecified items with reasonably good solutions is why many software engineers are well paid. It is also what makes our jobs more interesting than most, since it allows us to invoke our problem solving and design skills, which we generally prefer to rote execution of tasks.

I am not proposing that the engineers should fill in all the details without consulting the product managers and designers, I only mean that the engineers should expect the initial requirements will need to be refined. Ideally both will work to fill in the gaps, but the engineers should expect they will be the ones uncovering and explaining the gaps.

“I have yet to see any problem, however complicated, which, when you looked at it in the right way, did not become still more complicated.” — Poul Anderson

What is a “Product”?

Language is inherently imprecise. The same word can refer to completely different concepts at different times and yet it causes no confusion when the people conversing share the same contextual information. On the other hand, software engineers creating a data model have to explicitly enumerate, encode, and give names to all the concepts in the system. This is a fundamental difference between how the engineers and others view the problem and can be a source of frustration when engineers begin to inject questions into the requirements process such as: “What is a product?”. Those that are not accustomed to diving into the concepts underlying their use of a word can often feel like this is a time-wasting, philosophical discussion.

I’ve run across 8 distinct concepts where the word “product” has been used. The most basic difference lies between those “things” that you are trying to match and the “thing” you are using as the basis of the match. Suppose you get a data feed from Acme, Inc. which includes a thing called an “Acme Giant Rubber Band” and that you also crawled the Kwik-E-Mart web site, which yielded a thing called an “Acme Giant Green Rubber Band”. You then ask the question, are these the same “product”? Here we have an abstract notion of a specific rubber band in our mind and we are asking the question of whether these specific items from those two data sources match this concept.

Now let us also suppose that the “Acme Giant Rubber Band” item in the Acme data feed has listed 6 different UPC values, which correspond to 6 different colors they manufacturer for the product. This means that the “thing” in the feed is really a set of individual items, while the “Acme Giant Green Rubber Band” we saw on the Kwik-E-Mart web site just is a single item. These two items are similar, but not identical product-related concepts.

With just this simple example, there are 3 different concepts floating around, yet for each of them the “product” is often the word people will use. For most domains, when you really start to explore the data model that is required, more than three product-related concepts will likely be needed.

Software designers must carefully consider how many different “product” concepts they need to model and those helping to define the requirements should appreciate the importance of, and invest time in understanding the differences between the concepts. The importance of getting this data model correct from the start cannot be stressed enough.

“If names are not correct, then language is not in accord with the truth of things. If language is not in accord with the truth of things, then affairs cannot be carried out successfully.” — Confucius

Equality for All?

You should start with the most basic of questions: What is a “match”? My experience working on product matching in different domains and varying use cases is that there is not a single definition of product equality that applies everywhere. For those that have never given product matching much thought beyond their intuition, this might seem like an odd statement: two products are either the same or they are not, right? By way of example, here is an illustration of why different use cases require different notions of equality.

Suppose you are shopping for some 9-volt batteries and you are interested in seeing which brands tend to last longer based on direct user experience. You do a search, you navigate through some web site and then will likely need to make a choice at some point: are you looking to buy the 2-pack, the 4-pack or the 8-pack?

Having to make a quantity choice at this point may be premature, but you usually have to make this choice to get at the review content. However, the information you are looking for, and likely the bulk of the review content, is independent of the size of the box in which it is packaged. Requiring a quantity choice to get at review content may just be a bad user experience, but regardless of that, you certainly would not want to miss out on relevant review content simply because you had chosen the wrong quantity at this point in your research.

The conclusion here is that reviews posted to the web page for the 2-pack and reviews posted for the page of an 8-pack should probably not be fragmented. Therefore, for the purposes of review content, these two products, which would have different UPC and/or EAN values, should be considered equivalent.

Now suppose you have made your decision on the brand of battery to buy and now you are looking for the best price on an 8-pack. For a price comparison, you most definitely do not want to be comparing the 2-pack prices along with its 8-pack equivalent. Here, for price comparisons, these two products should definitely not be considered equivalent.

Understanding that product equivalence varies by context is not only important for designing algorithms and software systems, but has a lot of implications for creating better user experiences. For the companies looking to offer product matching as a service, the flexibility they offer in tailoring the definition of equality for their clients will be an important factor in how broadly applicable their solutions will be.

“It is more important to know where you are going than to get there quickly. Do not mistake activity for achievement.” — Isocrates

Imperfect Data Sources

If all the products you need to match have been assigned a globally unique identifier, such as a UPC, EAN or ISBN, and you have access to that data, and the data can be trusted, then product matching could be trivial. However, not all products get assigned such a number and for those that do, you do not always have access to those values. As discussed, it is also true that a “match” cannot always be defined simply by the equality of unique identifiers.

Those that crawl the web for product data tend to think that a structured data feed is the answer to getting better data. However, the companies that create product feeds vary greatly in their competency. Even when competent, they may build their feed from one system’s database, while more useful information may be stored in another system. Further, the competitive business landscape can result in companies wanting to deliberately suppress or obfuscate identifying information. You also have the ubiquitous issues of software bugs and data entry errors to contend with. All these realities add up to the fact that data feeds are not a panacea for product matching.

So while we have the web crawling folks wishing for feed data, we simultaneously have the feed processing folks wishing for crawled data to fill in their gaps. The first piece of advice for building a product matching system is to assume you will need to accept data from a variety of data sources. The ability to fill in data gaps with alternative sources will allow you to get the best of both worlds. This also means you may not only be trying to match products between different sites, but you may need to match products within the same site and merge the data from different sources to form a single view of a product at a site. I know of one very large shopping comparison site that did not design for this case and found themselves without the ability to support particular types of new business opportunities.

“If you think the problem is bad now, just wait until we’ve solved it.” — Arthur Kasspe

Look Before You Leap

The specific algorithms and technologies one chooses for an automated product matching system should not be the primary focus. It is very tempting for us information scientists and engineers to dive right into the algorithmic and technical solutions. After all, this is predominantly what universities have trained us to focus on and, in some sense, is the more interesting part of the problem. You can choose almost any one of a host of algorithms and get some form of product matching fairly quickly. Depending on your specific quality requirements, a simple system may be enough, but if there are higher expectations for a matching system, you will need a lot more than just a fancy algorithm.

When more than simple matching is needed, it will not be the algorithm you use, but how you use the algorithm that will matter. This means really understanding the characteristics of the problem in the context of your domain. It is also important not to define the problem too narrowly. There are a bunch of seemingly tangential issues in product matching that are very easy to put into the bucket of “we can deal with that later”, but which turn out to be very hard to deal with after the fact. It is how well you handle all of these practical details that will most influence the overall success of the project.

Choosing a simplistic data model is an example where it may seem like a good starting approach. However, this will wind up being so deeply ingrained in the software, that it will become nearly impossible to change. You wind up with either serious capability limitations or a series of kludges that both complicate your software and lead to unintended side effects. I learned this from experience.

“A doctor can bury his mistakes but an architect can only advise his clients to plant vines.” — Frank Lloyd Wright

Up Next

This posting covers some of the important characteristics of the product matching problem. In the sequel, there will be some more specific guidelines for building matching systems.