> For the complete documentation index, see [llms.txt](https://docs.activejs.dev/activejs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.activejs.dev/activejs/fundamentals/systems.md). # Systems Systems are nothing but a specialized combination of a few Units, a System creates a few predefined relationships among its member Units to make them part of a whole. While the Units are storage mediums, Systems are task helpers. A System tries to accomplish a specific type of task (*that has multiple aspects to it, and hence requiring multiple Units to work in cohesion*) in a reactive and shared fashion, such as data fetching using `XHR` API, or `fetch` API. Both of these APIs or any other asynchronous API more or less involve a **query**, a successful **response**, an **error**, and **pending-status** of the task. The [AsyncSystem](/activejs/fundamentals/systems/asyncsystem.md) is the System that is built to help with these kinds of asynchronous APIs. {% content-ref url="/pages/-M6aLGid7csUtSOcDjGY" %} [AsyncSystem](/activejs/fundamentals/systems/asyncsystem.md) {% endcontent-ref %} --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.activejs.dev/activejs/fundamentals/systems.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.