Monitor eBay Auctions with Visual Studio.NET

logging though mail earlier this year, I came across an interesting message about Microsoft and eBay working to make it easier to integrate eBay into Office applications. This piqued my interest, because anytime companies of this size start to work together, I take notice.

As developers, we all understand the importance of Microsoft, but eBay is a little bit different. It can be hard to understand why your company would need to interact with eBay until you look at the numbers. In case you haven't read the business pages lately, eBay has blown out its numbers again this quarter (Q1 2004). Digging a little deeper, you find that eBay really is, as they slogan says, "the world's marketplace." Some interesting eBay factoids include:

• One-third of people that have ever gone on the Internet have visited at sometime eBay.
• 25 percent of the German postal services traffic in 2002 was eBay related shipments.
• $23.8 billion(USD) in transactions are conducted on eBay in 2003. For Q1 of 2004 the number has risen to $8.0 billion for Q1 alone. This is about $1,000/sec.
• At anytime there are 21 million items on eBay, with three million items added each day.

The eBay API and SDK
While I don't sell many Beanie Babies, I have worked with people selling hundreds—if not thousands—of items on eBay. Now, these people could use the eBay Web interface to enter all their items, but it's a timely process and lacks integration with other systems the seller may use (inventory, order fulfillment, etc.). In business, time is money, so to facilitate application integration eBay provides two primary interfaces, the eBay API and the SDK.

The API is an XML-based interface. You communicate with eBay by creating a series of XML strings and passing them to the eBay processing DLL. This is the original interface and is still a primary means of application integration.

An alternative means of interfacing with eBay is the SDK. The SDK is a .NET library that wraps around and extends the API. The SDK handles all of the XML issues and operates in a manner more familiar to many object-oriented programmers, by using objects with methods and properties.