What Is the BizTalk Interoperability Framework?
The BizTalk interoperability framework consists of an application model. It also specifies BizTalk Document, Message, and Schema formats.
The BizTalk application model includes three logical "layers": the application layer, BizTalk server layer, and data communications services layer. (Note that the BizTalk specification uses the lowercase "s" to denote the BizTalk server logical layer to distinguish it from Microsoft's BizTalk Server product, which sports the uppercase "S".) These layers support transmission, processing, and receipt of BizTalk Messages.
In a BizTalk environment, line-of-business applications communicate among themselves by exchanging documents through one or more intermediate BizTalk servers. Applications and BizTalk servers may communicate over various data communications services or protocols, such as the HyperText Transfer Protocol (HTTP); File Transfer Protocol (FTP); or a message-brokering protocol, such as Microsoft Message Queue Server (MSMQ).
Under the BizTalk application model, an application is any system that fits all three of the following criteria. First, it stores and executes line-of-business data or processing logic. Second, it can generate and/or consume XML-formatted Business Documents. Third, it can communicate with a BizTalk server via a data communications service or protocol. The application may use an adapter "glue" layer to process XML and communicate with BizTalk servers. The application may support XML as one of its native file formats, or it may interface with adapter software that converts between XML and one or more of the application's native file formats.
The line-of-business application, or its BizTalk adapter, generates XML-formatted Business Documents—according to the appropriate, application-specific XML schema defined outside the BizTalk Framework. The application-adapter then wraps Business Documents and any associated binary file "attachments" with the XML "BizTags," both header and trailer, which define a "BizTalk Document" (per BizTalk schema defined in the BizTalk Framework). Then, the application submits the BizTalk Document to an originating BizTalk server.
BizTags provide BizTalk servers with document handling and routing information, acting as an "envelope" for the business information to be transmitted. They are the set of XML tags (both mandatory and optional) that are used to specify the handling of a Business Document—which is contained in a BizTalk Document, and which is in turn contained in a BizTalk Message. All BizTags are defined within standard BizTag namespaces with Uniform Resource Identifiers (URIs) derived by extension from the prefix http://schemas.biztalk.org/btf-2-0/. The BizTags are added as an XML envelope or wrapper around a Business Document by an application or BizTalk application-adapter. BizTags are processed by the BizTalk server or by other applications that facilitate the document interchange.
BizTalk servers provide various processing services to applications: validating, mapping, translating, encoding, encrypting, signing, routing, storing, forwarding, and delivering BizTalk Messages and BizTalk Documents. Any compliant BizTalk server can process any BizTag defined under BizTalk Framework 2.0. By contrast, the tags used to mark up business information within the BizTalk Message body are determined by application-specific XML document schemas. Application-specific document tags within a Business Document are not BizTags, and are generally not processed directly by the BizTalk server.
A BizTalk server receives a BizTalk Document sent by an application and then wraps this document within an electronic envelope that defines a "BizTalk Message." The envelope of a BizTalk Message—in other words, the specific non-BizTag headers and trailers used to enclose a BizTalk Document—is specific to each network transport protocol, such as HTTP, FTP, or MSMQ. Microsoft has not yet published its promised implementation guidelines for transport-specific envelopes for BizTalk Messages.
The typical end-to-end flow of a BizTalk Message consists of five principal processing steps:
A commerce-relevant event occurs within an application, thereby triggering business rules that spur creation of one or more Business Documents and (optional) binary file attachments.
The application, or its BizTalk adapter, transforms these Business Documents into a BizTalk Document by wrapping them with BizTags defined in the BizTalk schema (per specifications at http://www.biztalk.org/) and XML tags defined in application-specific schemas (per specifications defined at other industry schema-repository sites, such as http://www.xml.org).
The originating application transmits the BizTalk Document to the originating BizTalk server.
The originating BizTalk server creates a BizTalk Message by wrapping transport-specific envelope information around one or more Business Documents. The originating server uses addressing information contained in BizTags to determine the correct transport-specific destination address or addresses. The originating server then transmits the BizTalk Message to the destination BizTalk server over the appropriate transport protocol.
The destination BizTalk server validates the BizTalk Message, extracts the BizTalk Document contained within, validates it, and routes it to destination applications. Destination applications extract the Business Documents and optional binary file attachments contained in BizTalk Documents. Applications then process these documents and attachments according to application-specific business rules.
BizTalk applications differ from each other in several critical respects. First, applications may differ in the set of business rules implemented at end-point applications as well as intermediate BizTalk servers. Second, they may differ in the contents, schemas, and formats of Business Documents and binary file attachments they exchange. Third, they may differ in the end-to-end workflow process parameters encoded in BizTags in their BizTalk Documents. Fourth, they may differ in the platform-specific processing context in which each application or server processes a particular BizTalk Message or Document.
Indeed, there is a broad range of implementation-specific issues that come into play when you're developing an end-to-end BizTalk application. The principal implementation-specific issues are described in the following sections.
BizTalk Server Functionality
The BizTalk Framework does not specify the precise set of services to be provided by a generic BizTalk server. The scope of server functionality depends on the particular BizTalk server vendor's implementation. However, the BizTalk Framework strongly implies that these services will be provided to end-to-end applications from a homogeneous set of BizTalk servers, such as Microsoft's BizTalk Server product.
The BizTalk Framework does not specify the physical deployment of applications and BizTalk servers. Applications and BizTalk servers usually reside on separate machines, connected over local- and wide-area networks. However, they may also run on the same machine and communicate via various protocols over its internal bus.
The BizTalk Framework does not specify the communications protocols that bind applications and BizTalk servers to each other. Applications and servers may use any data communications network or protocol to communicate among themselves.
The BizTalk Framework does not specify the software interfaces between the application, BizTalk server, and data communications layers. These interfaces depend on the application programming interfaces (APIs), programming languages, and object models supported on the platforms on which these components are deployed.
The BizTalk Framework does not specify mechanisms for authentication, access control, encryption, tamper-proofing, or nonrepudiation on BizTalk Messages and their contents. Security on end-to-end BizTalk transactions depends on implementation-specific agreements on these issues.
Application State Information
The BizTalk Framework does not specify the way applications and BizTalk servers are supposed to define and communicate state information on in-process interchanges. State information defines the context of a particular Business Document within an end-to-end e-commerce transaction. However, BizTalk Framework 2.0 provides several BizTalk Message header fields for input of implementation-specific state information. These header fields consist of messageID, sent, state, referenceID, handle, process, and description.
As noted previously, the BizTalk Framework does not specify the operating environments on which line-of-business applications, BizTalk application-adapters, and BizTalk servers run. Operating environments constrain the physical-hosting, transport-protocol, software-interface, and state-information options available to BizTalk-enabled, line-of-business applications. However, the framework strongly implies that BizTalk implementers will develop or optimize their applications to run on Windows 2000 and associated Microsoft server software, especially Internet Information Server (IIS), Commerce Server, SQL Server, Microsoft Transaction Server (MTS), and MSMQ.
Business Document Schemas
The BizTalk Framework does not specify the schema—or information model—implemented in the contents of Business Documents. Microsoft has deliberately and wisely chosen not to dictate the logical structure of application-specific or vertical-market documents. Instead, the BizTalk Framework defers to other industry initiatives to define the XML schemas of business documents. BizTalk Documents can contain documents defined in vertical-market initiatives, such as the RosettaNet program that has defined XML schemas for business documents and online catalogs supporting the information-technology industry's supply chain. Similarly, the XML/EDI group is mapping existing American National Standards Institute (ANSI) X12 transaction sets to XML schemas. Microsoft has established an industry clearinghouse at http://www.biztalk.org for others to post application-specific or vertical-market XML document schemas that can be encapsulated in BizTalk Documents and Messages.
Workflow Process Definition and Execution
The BizTalk Framework does not contain specifications for defining end-to-end workflows involving BizTalk Messages. As a result, the framework does not live up to its promise of being able to encapsulate "self-describing" workflows within any given message transmitted between trading partners. The BizTalk Framework simply defines the header syntax of individual messages and the documents contained within them. These headers contain state information that hints at a BizTalk Message's role in a larger "interchange," a term that is largely synonymous with workflow or business process.
However, the headers by themselves do not specify the end-to-end sequence of processing steps through which one or more linked BizTalk Messages is to pass. If companies wish to implement interorganizational applications involving messages passed between two or more vendors' BizTalk servers, they will have to cobble together a very implementation-specific approach to defining, executing, and tracking these workflows.
Microsoft provides a tool and framework—the Commerce Interchange Pipeline—for defining e-commerce workflows involving a complex sequence of messages processed within a particular BizTalk server (Microsoft's own BizTalk Server product).
Event Model and Error Messages
The BizTalk Framework does not specify the event model to be shared and the error messages exchanged between BizTalk servers, BizTalk application-adapters, line-of-business applications, and data-communications interfaces. The event model should include standard alerts for a server, adapter, or application's inability to validate or process a BizTalk Message, BizTalk Document, or Business Document. The error messages should be standard XML documents that can be processed by BizTalk servers and application-adapters. Until Microsoft defines the BizTalk event model and error messages, these important features will remain implement-specific (in other words, proprietary features of Microsoft's BizTalk products and services).
Clearly, BizTalk's application model, as laid out in the BizTalk Framework 2.0 Independent Document Specification, provides only a general development framework. It is not a specification to which independent developers can write code without first addressing a broad range of implementation-specific issues. Consequently, a BizTalk application will not be easily portable to application environments other than the one to which they were written. As we've seen, Microsoft provides just such an application environment, the centerpiece of which is its BizTalk Server product.