Amazon Web Services

All it takes is a URL to start tapping in to the rich pool of resources made available by Web services.
Response Groups

As useful as the above information is, it still doesn't answer all of my original question, which is whether Amazon stocks the Pragmatic Programmers' book about Ruby on Rails, and how much it costs. I know that the Rails book is available from Amazon, but I don't know how much it costs. This is because ECS returns a small amount of data by default, corresponding to what we saw above. We can tailor the information that Amazon returns to us by specifying one or more response groups. Each response group corresponds to one or more types of data that ECS will return in its response.

To get basic pricing information about a book, we thus can ask to see the OfferSummary response group: http://webservices.amazon.com/onca/xml?Service=AWSECommerceService&Operation=ItemLookup&AWSAccessKeyId=XXX&ItemId=0735619530&ResponseGroup=OfferSummary“.

Instead of the previous listing, which described the book itself, we now get a list of the lowest new and used prices for a particular book. Here is the XML response from the above query:


<ItemLookupResponse>
<OperationRequest>
<HTTPHeaders>
<Header Name="UserAgent" Value="Mozilla/5.0 (Macintosh; U; PPC Mac
OS X Mach-O; en-US; rv:1.8) Gecko/20051111 Firefox/1.5"/>
</HTTPHeaders>
<RequestId>0SNXJ8T5V2JA18M8AJQC</RequestId>
<Arguments>
<Argument Name="ResponseGroup" Value="OfferSummary"/>
<Argument Name="Operation" Value="ItemLookup"/>
<Argument Name="Service" Value="AWSECommerceService"/>
<Argument Name="AWSAccessKeyId" Value="XXX"/>
<Argument Name="ItemId" Value="097669400X"/>
</Arguments>
<RequestProcessingTime>0.0331768989562988</RequestProcessingTime>
</OperationRequest>
<Items>
	<Request>
	<IsValid>True</IsValid>
	<ItemLookupRequest>
	<ItemId>097669400X</ItemId>
	<ResponseGroup>OfferSummary</ResponseGroup>
	</ItemLookupRequest>
	</Request>
	<Item>
	<ASIN>097669400X</ASIN>
	<OfferSummary>
	<LowestNewPrice>
	<Amount>2295</Amount>
	<CurrencyCode>USD</CurrencyCode>
	<FormattedPrice>$22.95</FormattedPrice>
	</LowestNewPrice>
	<LowestUsedPrice>
	<Amount>2341</Amount>
	<CurrencyCode>USD</CurrencyCode>
	<FormattedPrice>$23.41</FormattedPrice>
	</LowestUsedPrice>
	<LowestCollectiblePrice>
	<Amount>3495</Amount>
	<CurrencyCode>USD</CurrencyCode>
	<FormattedPrice>$34.95</FormattedPrice>
	</LowestCollectiblePrice>
	<TotalNew>41</TotalNew>
	<TotalUsed>12</TotalUsed>
	<TotalCollectible>2</TotalCollectible>
	<TotalRefurbished>0</TotalRefurbished>
	</OfferSummary>
	</Item>
</Items>
</ItemLookupResponse>

As you can see, the initial portion of the response is the same. But the second half of the response, inside of the <Items> tag, is different, with LowestNewPrice, LowestUsedPrice and LowestCollectiblePrice tags showing us how much we can buy this book for.

We also can ask for other response groups, mixing and matching their names as necessary. For example, we can request the Medium response group, giving us not only information about the request and the book, but also the images (in a number of sizes) associated with the book, the book's size and weight, and editorial reviews. If we want to go beyond that, getting reviews of the book that have been left by Amazon customers and lists of similar products, we can request the Large response group.

Summary

Amazon's Web services provide us with a tool to look through a huge database of product information, for both personal and commercial use. In addition, ECS gives us a taste of what it is like to create REST-style queries, and how we might parse the results. Finally, just as Web developers often learn from the HTML and JavaScript on existing sites, we can learn how to create good Web services for our own use by studying the way in which Amazon has done theirs. In particular, I like Amazon's concept of response groups, which allows us to mix and match the types of responses we might get—something that I may well emulate in my own Web services.

Next month, we'll build on what we saw here, creating a Web service of our own that aggregates data from Amazon and my local public library to give me a personalized book lookup system.

Resources for this article: /article/8748.

Reuven M. Lerner, a longtime Web/database consultant, is a PhD student in Learning Sciences at Northwestern University. He lives outside of Chicago with his wife and three children, including newborn son, Amotz David.

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Amazon web services book

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