INTRODUCTION

As with everything else, we have a very holistic view of metadata and discovery features, looking at the entire reference model described in Chapter 3 and shown in Figure 3.1. In this chapter, we describe all different kinds of metadata that are relevant for a complete orchestration environment. We discuss the role of service discovery facilities and describe what is expected from those facilities.

The role of metadata and service discovery is generally well understood in a service-oriented architecture. Figure 7.1 illustrates the typical publish–discover–bind cycle. A new business service is developed. Its developers publish the service contract in the business registry. The service consumers discover the service from the registry, bind to it, and use the service. In this typical service-oriented architecture, the service contract consists primarily of the service description. This service-level information is generally categorized using some taxonomy scheme. A service consumer either searches the service by name or looks for a service that implements some particular specification.

Although these roles of metadata and service discovery are still true for a complete BSO environment, the metadata for the BSO environment are significantly more complex than what was described above, and service discovery requires some additional capabilities as well.

Metadata can actually be split into four broad categories:

1. Descriptive metadata. These metadata include service contracts, orchestration definitions, and messages data types.

2. Rules. An important part of metadata is various kind of data validation and data transformation rules that have been defined for successfully execute orchestrations.

3. […]