Archive for the ‘taxonomy’ Tag

Taxonomy for Web Service Sources

Various taxonomies for web services are possible.  A focus on technology might produce classifications such as transport (e.g., HTTP, JMS), representation (e.g., SOAP, REST), response handling (e.g., blocking, asynchronous via polling, asynchronous via callback).  A focus on purpose might look more like data source vs. computational vs. legacy API exposure.

In the Web 2.0+ era, web services are proliferating wildly.  The mashup community is providing huge demand satisfied in part by sites such as ProgrammableWeb where over 1,000 web services can be found, and increasingly online services are opening their platforms via APIs.  Enterprise level SOA (Service Oriented Architecture) initiatives, while slowed by a slowing economy, are also beginning to consume external services as well as exposing their own services for internal use.

In recognition of this proliferation, I believe a new taxonomy is required that addresses the source of services from the perspective of the user, orthogonal to technology or purpose.  By “user” in this context, I am referring to the human developer of any application that consumes web services.

Source Taxonomy

The figure illustrates a draft web service taxonomy where services are classified by the nature of their sources or providers as seen by potential users.

ws-source-taxonomy

Classification:  Ownership

Ownership is the distinction between services that are sourced within the user’s organization (e.g., company, business unit) versus those sourced by parties unaffiliated with their organization.

Internal:  “Services sourced within the user’s organization implying some potential for control over their implementation.”  Examples include web service APIs to internal legacy systems as part of a SOA project.

External:  “Services sourced independent of the user’s organization.”  Examples include information services (e.g., news, market quotes, credit report) and APIs to platforms like Twitter or SalesForce.

Classification:  Provision

Provisioning refers to the relationship between the entity supporting the web service endpoint from the user’s perspective (i.e., the provider) and the entity that supplies the functional implementation of the web service (i.e., the source).  When the provider is the source, the service is said to be original.  Conversely, if the provider is some form of third party intermediary between user and source, the service is said to be syndicated.

External / Original:  “External services that are called directly by a user’s application.”

External / Syndicated:  “External services for which users call a third party provider or syndicator which would then call the original source on their behalf.”  Presumably in this type of structure, the syndicator would add some value for acting as intermediary.  For example, a syndicator could serve as a common front for many original service sources thereby presenting an additional interface abstraction and a common point of billing and support.

Internal / Original vs. Syndicated:  Based on the foregoing definitions, the notion of a syndicated internal service seems oxymoronic.  The taxonomic intent is to enable larger enterprises to make the distinction, for example, between point-to-point calling of a legacy API (i.e., original source) versus the use of an intermediate hub, messaging service, or some other abstraction layer (i.e., a form of syndication).

Classification:  Differentiation

This classification addresses the potential for multiple sources to provide functionally equivalent services and how the user perceives the relative value of those sources.  A service is referred to as a commodity if it is possible for multiple sources to provide functionally equivalent implementations of that service, whether or not multiple such sources actually exist.  In contrast, a service is referred to as branded if there can be only one source of that service.

External / Original / Commodity:  “Services provided by an original source that can also be offered by other sources.”  The functional equivalence of these services can enable a user to select a source based on non-functional factors such as price, performance, and reliability.  Examples might include data services such as weather or financial market data.  In this scenario, the commodity sourcing decision must be performed by the user.  Despite functional equivalence, each source may present differing interfaces to which the user must code.

External / Syndicated / Commodity:  “Services provided by a syndicator fronting for potentially multiple functionally equivalent sources.”  The key value of commodity syndication lies in the fact that functional equivalence does not imply interface equivalence.  For a given commodity service, a commodity syndicator has the opportunity to normalize interfaces across functionally equivalent sources, thus providing the user with a single stable interface per service.  This scenario would support the commodity sourcing decision being made either by the user or transparently by the syndicator.

External / Original / Branded:  “Services provided by an original source that can only be available from that source.”  The most common types of these services are APIs to specific applications or platforms.  For example, consider writing a mashup for your back office that uses the SalesForce API.  It cannot decide lightly to call a different CRM application since it is highly unlikely that its API will be functionally equivalent at the service level, not to mention the fact that your company’s data lives at SalesForce.

External / Syndicated / Branded:  “Services that can only be available from a single source, but are accessed through a syndicator.”  This class is included for taxonomic completeness although it is unclear what significant value the syndicator would provide in this case.  There may be some value in a single gateway to multiple branded services for billing, support, or auditing purposes, but this alone hardly seems compelling relative to the overhead.

Classification:  Session

This classification recognizes that certain logical operations may require multiple web service calls.  While this may seem like a technical distinction, its relevance to this taxonomy is in the context of commodity source selection.

… / Commodity / Stateless:  “Completely independent web service calls enabling commodity sourcing decisions on a per call basis if desired.”  This is the finest granularity of web service commoditization.  An example of this might be a request for a stock quote for a known ticker symbol.  A single call does the job and there is any number of functionally equivalent service sources for this information.

… / Commodity / Statefull:  “A logically related group of web service calls that all must be made to the same source, thus necessitating a single commodity sourcing decision for the group.”  An example might be obtaining a credit report on a company.  A first call requests a “list of similars” based on the company name.  The returned list includes a set of possible matches with additional data for disambiguation and source specific IDs.  After selecting the desired company from the list, the second call requests the actual report based on the ID.  The user may not care which source is used, but having made the sourcing decision for the first call, the rest of this conversation must return to the same source since it carries source specific information.

Summary

The last 5 years have seen the rapid proliferation of available web services and a growing appetite of Web 2.0+ developers anxious to consume them.  Thus far, the focus has been on what mashups and service oriented applications can do and how to achieve them functionally.  Going forward, we will see increased attention to qualities of service, stability, and source redundancy analogous to that of cloud computing.  Lack of maturity in these areas is among the factors holding back enterprises from full scale consumption of external web services in their business applications.  Concepts such as syndication and commoditization can play a key role in breaking through this barrier.

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