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Integration at the Edge
The enterprise service bus erases the distinction among internal and external networks for supply-chain applications
by David Chappell

Posted May 26, 2004

For the past decade, throughout the era of enterprise application integration (EAI) and the evolution of the Internet and application server technology, a clear dividing line has developed. This line separates the communications and application integration infrastructure within the four walls of a corporation and external communications with business partners, vendors, and customers.

This separation has been driven largely by the capabilities and limitations of the technology. To date, technology such as application server infrastructure is specifically designed to make clear distinctions between what's inside the firewall versus what's outside the firewall. This distinction is evidenced by completely separate architectural approaches, with different programming models required for building applications. In the J2EE application server architecture, for example, this approach is manifested as a Web container versus an EJB container.

Hub-and-spoke EAI brokers could get as far as the corporate boundaries, but were not really built well for scaling beyond that. Various bridging technologies are designed to bridge the gap at the edge of the network. In many legacy cases, this technology is bolted on as an afterthought. The majority of the effort being done to date in the area of Web services has also been focused on this edge of the network.

But just exactly where is the edge of the network? Before we answer that, let's explore another forbear of the enterprise service bus (ESB), the e-marketplace, also known as the e-commerce trading hub (see the sidebar, "ESB").

e-Commerce Trading Hubs
In a trading network of business partners, companies desire to move away from expensive, EDI, value-added networks and use the public Internet as a means of communications among entities, wherever possible, and to lower the barrier to entry for participation such that small-to-medium enterprises can afford to participate. This desire was the impetus behind the creation of e-marketplaces and trading exchanges such as those powered by CommerceOne and GE Global Exchange Services (GXS).

A trading exchange acts as an intermediary, or semiprivate business portal, that facilitates electronic commerce between buyers and suppliers in a supply chain (see the sidebar, "Case Study: ESB in the Supply Chain"). The majority of the interactions with the portal are not browser based—the interactions are done directly among specialized applications that require little or no human interaction. The interactions happen between applications residing at the trading partner and back-end applications that reside in the trading hub. These back-end trading hub applications provide value-added functions such as dispersion of request for quotes (RFQs) between a buyer and multiple suppliers or availability to promise (ATP) data from suppliers to buyers (see Figure 1).

This environment introduced some rather challenging requirements, some of which seemed at odds with each other. For example, this scenario requires secure access between the applications residing at the partner sites, and the applications residing in the trading partner hub, using the public Internet as the vehicle for communication. This scenario also required reliable messaging, yet the traditional message-oriented middleware (MOM) vendors did not have a MOM infrastructure that was capable of spanning across the public Internet in a scalable and secure fashion.

The suppliers communicating through a trading hub are often fierce competitors with each other, so it is imperative that they not be able to see each other's data such as pricing information. This consideration requires full authentication and access control between the trading partners and the trading hub. Functionality in the trading hub must be exposed to trading partners through a service interface. A supplier must also be able to freely share its data with the trading hub, and the trading hub applications must selectively be able to pass that data along to buyers, but not to other suppliers competing for the same business. A supplier must never be able to masquerade as another supplier and get access to its sensitive data.