Add initial drafts of high-level design docs

README.md

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+# Component Model design and specification
+
+This repository contains documents describing the high-level [goals],
+[use cases], [design choices] and [FAQ] of the component model.
+
+In the future, as proposals get merged, the repository will additionally
+contain the spec, a reference interpreter, a test suite, and directories for
+each proposal with the proposal's explainer and specific design documents.
+
+## Design Process & Contributing
+
+At this early stage, this repository only contains high-level design documents
+and discussions about the Component Model in general. Detailed explainers,
+specifications and discussions are broken into the following two repositories
+which, together, will form the "MVP" of the Component Model:
+
+* The [module-linking] proposal will initialize the Component Model
+  specification, adding the ability for WebAssembly to import, nest,
+  instantiate and link multiple Core WebAssembly modules without host-specific
+  support.
+
+* The [interface-types] proposal will extend the Component Model specification
+  with a new set of high-level types for defining shared-nothing,
+  language-neutral "components".
+
+All Component Model work is done as part of the [W3C WebAssembly Community Group].
+To contribute to any of these repositories, see the Community Group's
+[Contributing Guidelines].
+
+
+[goals]: design/high-level/Goals.md
+[use cases]: design/high-level/UseCases.md
+[design choices]: design/high-level/Choices.md
+[FAQ]: design/high-level/FAQ.md
+[module-linking]: https://github.com/webassembly/module-linking/
+[interface-types]: https://github.com/webassembly/interface-types/
+[W3C WebAssembly Community Group]: https://www.w3.org/community/webassembly/
+[Contributing Guidelines]: https://webassembly.org/community/contributing/

design/LICENSE

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design/README.md

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+See the [parent README](../README.md).

design/high-level/Choices.md

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+# Component Model High-Level Design Choices
+
+Based on the [goals](Goals.md) and [use cases](UseCases.md), the component
+model makes several high-level design choices that permeate the rest of the
+component model.
+
+1. The component model adopts a shared-nothing architecture in which component
+   instances fully encapsulate their linear memories, tables, globals and, in
+   the future, GC memory. Component interfaces contain only immutable copied
+   values, opaque typed handles and immutable uninstantiated modules/components.
+   While handles and imports can be used as an indirect form of sharing, the
+   [dependency use cases](UseCases.md#component-dependencies) enable this degree
+   of sharing to be finely controlled.
+
+2. The component model introduces no global singletons, namespaces, registries,
+   locator services or frameworks through which components are configured or
+   linked. Instead, all related use cases are addressed through explicit
+   parametrization of components via imports (of data, functions, and types)
+   with every client of a component having the option to independently
+   instantiate the component with its own chosen import values.
+
+3. The component model assumes no global inter-component garbage or cycle
+   collector that is able to trace through cross-component cycles. Instead
+   resources have lifetimes and require explicit acyclic ownership through
+   handles. The explicit lifetimes allow resources to have destructors that are
+   called deterministically and can be used to release linear memory
+   allocations in non-garbage-collected languages.
+
+4. The component model assumes that Just-In-Time compilation is not available
+   at runtime and thus only provides declarative linking features that admit
+   Ahead-of-Time compilation, optimization and analysis. While component instances
+   can be created at runtime, the components being instantiated as well as their
+   dependencies and clients are known before execution begins.
+   (See also [this slide](https://docs.google.com/presentation/d/1PSC3Q5oFsJEaYyV5lNJvVgh-SNxhySWUqZ6puyojMi8/edit#slide=id.gceaf867ebf_0_10).)

design/high-level/FAQ.md

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+# FAQ
+
+### How does WASI relate to the Component Model?
+
+[WASI] is layered on top of the Component Model, with the Component Model
+providing the foundational building blocks used to define WASI's interfaces,
+including:
+* the grammar of types that can be used in WASI interfaces;
+* the linking functionality that WASI can assume is used to compose separate
+  modules of code, isolate their capabilities and virtualize WASI interfaces;
+* the core wasm ABI that core wasm toolchains can compile against when targeting WASI.
+
+By way of comparison to traditional Operating Systems, the Component Model
+fills the role of an OS's process model (defining how processes start up and
+communicate with each other) while WASI fills the role of an OS's many I/O
+interfaces.
+
+Use of WASI does not force the client to target the Component Model, however.
+Any core wasm producer can simply target the core wasm ABI defined by the
+Component Model for a given WASI interface's signature. This approach reopens
+many questions that are answered by the Component Model, particularly when more
+than one wasm module is involved, but for single-module scenarios or highly
+custom scenarios, this might be appropriate.
+
+
+[WASI]: https://github.com/WebAssembly/WASI/blob/main/README.md

design/high-level/Goals.md

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+# Component Model High-Level Goals
+
+(For comparison, see WebAssembly's [original High-Level Goals].)
+
+1. Define a portable, load- and run-time-efficient binary format for
+   separately-compiled components built from WebAssembly core modules that
+   enable portable, cross-language composition.
+2. Support the definition of portable, virtualizable, statically-analyzable,
+   capability-safe, language-agnostic interfaces, especially those being 
+   defined by [WASI].
+3. Maintain and enhance WebAssembly's unique value proposition:
+   * *Language neutrality*: avoid biasing the component model toward just one
+     language or family of languages.
+   * *Embeddability*: design components to be embedded in a diverse set of
+     host execution environments, including browsers, servers, intermediaries,
+     small devices and data-intensive systems.
+   * *Optimizability*: maximize the static information available to
+     Ahead-of-Time compilers to minimize the cost of instantiation and
+     startup.
+   * *Formal semantics*: define the component model within the same semantic
+     framework as core wasm.
+   * *Web platform integration*: ensure components can be natively supported
+      in browsers by extending the existing WebAssembly integration points: the
+      [JS API], [Web API] and [ESM-integration]. Before native support is
+      implemented, ensure components can be polyfilled in browsers via
+      Ahead-of-Time compilation to currently-supported browser functionality.
+4. Define the component model *incrementally*: starting from a set of
+   [initial use cases] and expanding the set of use cases over time,
+   prioritized by feedback and experience.
+
+## Non-goals
+
+1. Don't attempt to solve 100% of WebAssembly embedding scenarios.
+   * Some scenarios will require features in conflict with the above-mentioned goal.
+   * With the layered approach to specification, unsupported embedding
+     scenarios can be solved via alternative layered specifications or by
+     directly embedding the existing WebAssembly core specification.
+2. Don't attempt to solve problems that are better solved by some combination
+   of the toolchain, the platform or higher layer specifications, including:
+   * package management and version control;
+   * deployment and live upgrade / dynamic reconfiguration;
+   * persistence and storage; and
+   * distributed computing and partial failure.
+2. Don't specify a set of "component services".
+   * Specifying services that may be implemented by a host and exposed to
+     components is the domain of WASI and out of scope of the component model.
+   * See also the [WASI FAQ entry](FAQ.md#how-does-wasi-relate-to-the-component-model).
+
+
+[original High-Level Goals]: https://github.com/WebAssembly/design/blob/main/HighLevelGoals.md
+[WASI]: https://github.com/WebAssembly/WASI/blob/main/README.md
+[JS API]: https://webassembly.github.io/spec/js-api/index.html
+[Web API]: https://webassembly.github.io/spec/web-api/index.html
+[ESM-integration]: https://github.com/WebAssembly/esm-integration/tree/main/proposals/esm-integration
+[initial use cases]: UseCases.md#Initial-MVP

design/high-level/README.md

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+# Component Model High-Level Design Documents
+
+This directory contains design documents describing the component model's
+[goals](Goals.md), [use cases](UseCases.md), [design choices](Choices.md)
+and [FAQ](FAQ.md).