Understanding the Core Concepts

Welcome to the conceptual overview of our platform. This section dives deep into the fundamental ideas and architectural principles that underpin our services and products. Understanding these concepts is crucial for effectively utilizing our tools and building robust applications.

1. The Entity Model

At the heart of our system lies the Entity Model. An entity represents a distinct, addressable object within our domain. These can be anything from users and projects to resources and configurations.

Key characteristics of an entity include:

A unique identifier (ID).
A set of properties that describe its state.
Relationships with other entities.

We abstract entities to provide a consistent way to interact with various data types. This allows for generalized operations like CRUD (Create, Read, Update, Delete) across different kinds of data.

1.1 Properties and Attributes

Each entity is composed of properties, which are key-value pairs representing its attributes. These can be primitive types (strings, numbers, booleans) or complex objects and lists.

Note: Property names are case-insensitive for compatibility, but we recommend using consistent casing (e.g., camelCase) in your code.

1.2 Relationships

Entities can be related to one another. These relationships are typically defined by referencing the ID of another entity. Common relationship types include:

One-to-One: An entity is related to at most one other entity.
One-to-Many: An entity can be related to multiple other entities.
Many-to-Many: Multiple entities can be related to multiple other entities.

Understanding relationships is key to navigating and querying interconnected data effectively.

2. The State Machine

Many of our services operate on a state-driven model. The State Machine is a conceptual framework that defines a set of possible states an entity can be in, and the transitions that can occur between these states.

Transitions are triggered by events and often involve performing actions or validating certain conditions. This ensures predictable behavior and data integrity.

2.1 States and Transitions

A state represents a particular condition or status of an entity. A transition is a movement from one state to another, usually in response to a specific event or action.


{
  "entityType": "Order",
  "initialState": "Pending",
  "states": ["Pending", "Processing", "Shipped", "Delivered", "Cancelled"],
  "transitions": [
    { "from": "Pending", "to": "Processing", "event": "processOrder" },
    { "from": "Processing", "to": "Shipped", "event": "shipOrder" },
    { "from": "Shipped", "to": "Delivered", "event": "confirmDelivery" },
    { "from": "Pending", "to": "Cancelled", "event": "cancelOrder" },
    { "from": "Processing", "to": "Cancelled", "event": "cancelOrder" }
  ]
}

2.2 Events and Actions

Events are notifications that something has happened, which may trigger a state transition. Actions are operations performed as part of a state transition, such as updating properties or calling external services.

Tip: Carefully designing your states and transitions helps in building robust, predictable, and auditable systems.

3. The API Gateway

All interactions with our services are managed through a central API Gateway. This acts as the single entry point for all client requests, abstracting away the underlying microservices architecture.

The API Gateway is responsible for:

Request Routing: Directing incoming requests to the appropriate microservice.
Authentication and Authorization: Verifying the identity and permissions of the client.
Rate Limiting: Protecting services from overload.
Request/Response Transformation: Adapting requests and responses for different services.

By using the API Gateway, developers don't need to worry about the complexity of individual microservices. They interact with a unified interface.

4. Data Consistency and Concurrency

Ensuring data consistency and handling concurrent operations are critical challenges in distributed systems. We employ several strategies to address these:

Optimistic Concurrency Control (OCC): We use versioning (e.g., `_rev` fields) to detect concurrent modifications. If a conflict is detected, the operation fails, and the client must re-fetch and retry.
Idempotency: API operations are designed to be idempotent where possible, meaning that making the same request multiple times has the same effect as making it once. This is crucial for reliable retries.
Transactions: For operations requiring atomicity across multiple entities, we provide transactional mechanisms.

4.1 Versioning

Each entity typically has a version identifier. When updating an entity, you must provide the current version. If the version on the server is different, it indicates that another process has modified the entity since you last read it, leading to a concurrency conflict.


# Example of an update request with version
PUT /entities/12345
{
  "_rev": "v3",
  "propertyName": "newValue"
}

Conclusion

These core concepts form the foundation of our platform. By grasping the Entity Model, State Machine principles, API Gateway role, and our approaches to data consistency, you'll be well-equipped to build powerful and reliable applications with our services.