At the Forge - Google Web Services
For the past few months, we've been looking at a number of Web services offered by Amazon, allowing us to search through its catalog with relative ease. Amazon decided several years ago to make its Web services largely free, on the assumption that this would raise the number of people eventually buying from its Web site. And indeed, a large number of developers now use Amazon Web services to create everything from custom bookstores to programs that can help with bookstore management.
Amazon isn't the only commercial Web site that has opened up its catalog to the outside world. Google, another 900-pound Internet gorilla, also released its Web APIs several years ago. These APIs make it possible to search through Google's extensive catalog of Web content. It's impossible to know whether this catalog is the largest in the world, but from my perspective, that's somewhat irrelevant. Google's catalog is large enough, and is updated frequently enough, for me to rely on it as my primary search engine most of the time.
Google has made a number of different APIs available over the last few years. This month, we look at the simplest of them, for performing basic searches of the Web archive. We examine how Google uses WSDL (Web service description language) to advertise its Web services and how we can make SOAP calls to search through Google's extensive library for our own purposes.
If you have worked with Amazon Web services, getting started with Google's APIs will not surprise you a great deal. To begin, both companies require that you register to use their services. Registration is free in both cases and provides you with an identification key that is placed in every request to the server.
To obtain a Google key, you first need to register for a Google account. Now, I've had a “Google account” for some time, for use with services such as Gmail and its personalized news page. However, it seems the APIs are linked to a different set of accounts. The fact that I had to register and log in to the API system, even after initially logging in to my “main” Google account, struck me as a bit odd.
That said, creating an account is simple and straightforward. Go to the main Google API page (www.google.com/apis), click on create a Google account, and fill out the form. Soon after submitting the HTML form, you will receive e-mail from Google confirming the creation of your account and containing your Google key, along with a URL to visit in order to confirm the account's creation. After confirming the creation of your account, you're ready to move forward with the use of your Google key, creating programs that take advantage of Google's Web services.
Before we do that though, we should consider the restrictions that Google places on the service and the data we retrieve through it. Amazon allows participants to make only one API call per second, which means a maximum of 86,400 calls in a given 24-hour period. Google, by contrast, allows users to make only 1,000 calls in a given 24-hour period.
Moreover, the way in which these maximums are defined indicates the way in which violations will be handled. Google will return an error message if you have made more than 1,000 queries in the previous 24 hours, whereas Amazon will complain only if a query comes within one second of a previous query. Neither service keeps track of these numbers before returning an error message, but it is obviously easier to recover from violating Amazon's restrictions (by sleeping for one second and retrying) than Google's (as the program might need to sleep for up to 24 hours before retrying).
There are a number of legal differences between the two sites' services. Amazon pioneered the idea of affiliate vendors on the Web, encouraging people to create commercial services around its database. By contrast, Google explicitly states that users are forbidden from creating a commercial service around its search results. (If you are interested in creating a commercial service based around Internet search data, consider looking at Amazon's Alexa Web search platform service, which doesn't have these restrictions. At the same time, it'll cost you 25 cents for every 1,000 requests, which can add up quickly for a popular site.)
Finally, there are some technical differences between the two sites. Amazon's APIs work via both SOAP and REST, allowing developers to choose between these two formats. Google, by contrast, provides only a SOAP interface to its search engine. So, in order to create our search system, we need to install and use a SOAP client library. Fortunately, most languages have high-level libraries that allow for SOAP calls.