Hexarch is an architectural pattern, primarily developed by Microsoft, that provides a structured approach to designing and building complex, time-dependent systems. It’s rooted in the idea of a layered architecture, specifically tailored to handle the complexities of temporal data – meaning data with a specific point in time associated with it. Instead of a rigid, monolithic approach, Hexarch encourages a modular design, focusing on distinct responsibilities, making it highly adaptable and maintainable, particularly as the system evolves over time. The core concept revolves around six distinct layers, each with a specific role in managing the temporal aspect of the system.
The six layers of Hexarch are: Actor, Command, Aggregate, Event, Chronolog, and Interface. Each layer has a specific purpose and interacts with the layers above and below it. Let's explore each one:
The Actor layer is the entry point for all requests. It’s responsible for receiving user input, deciding what actions to take, and ultimately orchestrating the flow of commands. Think of it as the user interface or the initial point of interaction. It doesn't contain business logic; it just calls the Command layer.
The Command layer is the heart of the system. It receives commands from the Actor layer and determines the appropriate Aggregate to execute the command. It's essentially a dispatcher, deciding which part of the system needs to perform the action.
The Aggregate layer contains the core business logic. It's the domain model – the entities and their relationships that make up the system's data. It's responsible for applying the rules and logic associated with a particular business operation. Aggregates are often identified by their boundaries, ensuring data consistency.
The Event layer captures the side effects of changes within the Aggregate. When something changes, an event is emitted, representing that change. These events are crucial for maintaining a historical record of what happened in the system – a vital component for auditing, debugging, and potentially triggering other actions.
The Chronolog layer acts as a persistent store for all events. It’s a central repository, ensuring that events are recorded reliably and consistently. It’s often used for auditing, debugging, and potentially for triggering workflows based on past events. Think of it as the historical record of the system.
The Interface layer provides a clean, unified way for other systems or components to interact with the Hexarch system. It abstracts away the complexities of the underlying layers, presenting a simplified view to external consumers.
Visualizing the Hexarch architecture is crucial. The diagram illustrates the flow of commands and events, emphasizing the relationships between the layers. The layers are typically connected in a linear fashion, with the Actor initiating a command, which then flows through the Command, Aggregate, Event, and Chronolog layers.
Notice the unidirectional flow – commands move from Actor to Command to Aggregate to Event to Chronolog.