Software Architecture

Transactional Saga Patterns

In Chapter 2, we introduced a matrix that juxtaposed each of the intersecting dimensions when architects must choose how to implement a transactional saga, reproduced in Table 12-1.

Table 12-1. The matrix of dimensional intersections for distributed architectures Pattern name	Communication	Consistency	Coordination
Epic Saga(sao)	Synchronous	Atomic	Orchestrated
Phone Tag Saga(sac)	Synchronous	Atomic	Choreographed
Fairy Tale Saga(seo)	Synchronous	Eventual	Orchestrated
Time Travel Saga(sec)	Synchronous	Eventual	Choreographed
Fantasy Fiction Saga(aao)	Asynchronous	Atomic	Orchestrated
Horror Story(aac)	Asynchronous	Atomic	Choreographed
Parallel Saga(aeo)	Asynchronous	Eventual	Orchestrated
Anthology Saga(aec)	Asynchronous	Eventual	Choreographed

We provide whimsical names for each combination, all derived from types of sagas. However, the pattern names exist to help differentiate the possibilities, and we don’t want to provide a memorization test to associate a pattern name to a set of characteristics, so we have added a superscript to each saga type indicating the values of the three dimensions listed in alphabetical order (as in Table 12-1). For example, the Epic Saga(sao) pattern indicates the values of synchronous, atomic, and orchestrated for communication, consistency, and coordination. The superscripts help you associate names to character sets more easily.
While architects will utilize some of the patterns more than others, they all have legitimate uses and differing sets of trade-offs.
We illustrate each possible communication combination with both a three-dimensional representation of the intersection of the three forces in space along with an example workflow using generic distributed services, which we refer to as isomorphic diagrams. These diagrams show interactions between services in the most generic way, toward our goal of showing architect concepts in the simplest form. In each of these diagrams, we use the set of generic symbols shown in Figure 12-1.

Figure 12-1. Legend for ISO architecture interaction diagrams

For each of the architecture patterns, we do not show every possible interaction, which would become repetitive. Instead, we identify and illustrate the differentiating features of the pattern—what makes its behavior unique among the patterns.