In the following blog which refers to the Amazon CEO's "letter to the share holders" one is truly amazed to read about how the Amazon team constructs a single product detail page from a combination of 200 to 300 services!!
Amazon architects may have truly found a way to identify the right level of service granularity to combine these into composite service offerings - without causing the information in the combined service to be distorted. This so called semantic dissonance has led many of us architects to create coarse grained services which preserve the quality of information but at the cost of reuse!
This is the the balancing act of how to define a service with the right grain of information encapsulated in it such that once it is combined with another service the combined service is still able to deliver meaningful information at the same grain of the originally combined services. This is what we mean by semantics that govern how to combine two or more granular services to create a meaningful composite service which continues to encapsulate information that is valid and accurate. It may be technically possible to create a composite or a single course grained service starting from two granular services (long as the canonical models/ payload have common elements) but the combination may overlook key business constraints, business rules, regulations and algorithms that render the final response invalid and inaccurate.
A very simple example, combining product sales of a region with product marketing dollars to yield a service that delivers marketing efficacy may be a great new service concept. However, if the product sales service does not provide information about the tenure of the product company by region or the presence of similar competitor products by region then the marketing efficacy service is not able to account for lift in the sales accurately. The reason being marketing efficacy service cannot appropriately reflect the efficacy of the marketing dollar as being attributed to the "novelty" factor (where in the product is the first to enter the market in this region, or else if the product has a very attractive "entry price point" as it's debut to this new region). Both of these artificially show that the marketing campaign strategy is far more successful than it might really be. The price and novelty had more to do with the sales lift.
The use of information by the business to make strategic decisions and the study of information flow across lines of business and the alignment of business information to strategic business activities is key to business architecture. By extension we find that it is in the realm of business architecture to govern service interactions and the creation of composite strategies to guard against semantic dissonance.
Please share with me your thoughts.