XPS Architecture

XPS is based upon a set of libraries and executables that provide a whole programming environment. XPS is also based on various other software components. This page will eventually describe those components and their inter-relationships.

Overview

The diagram above shows a rough architecture of XPS. At the foundational layer are external software packages: LLVM, APR, etc. On top of those packages XPS provides a set of libraries: base, xml, cfg, etc. From those libraries a set of tools are constructed: XPLC, XVM, etc. The sections that follow describe each of these categories and their components

External Libraries

LLVM

The Low Level Virtual Machine is a compiler writer's infrastructure providing the following features that XPS uses:

• a low level intermediate representation (IR) in assembly, bytecode and C++ forms
• various analyses including alias analysis, data structure, and control flow
• an infrastructure for writing module, function, and basic-block level passes for transformation of code
• A plethora of optimization passes for both compile time and link time.
• back ends to generate code for "C", x86, SPARC, and PowerPC. More targets are being written.
• a variety of tools including source-level debugger, compiler driver, linker, assembler, disassembler, etc.

LLVM is fully documented here
. XPS uses LLVM as its low level representation of programs and for code generation and execution services.

APR

The Apache Portable Runtime is the basis for the runtime environment. This runtime is in use in the Apache httpd web server and provides a portable toolkit for operating system services and other software packages.
XPS uses APR to shield itself from differences in operating systems and to ensure stable semantics for the operations provided across platforms.

eXpat

The eXpat XML parser provides basic XML parsing services. It manages character set translation, recognition of well-formed documents, and management of namespace processing. All of XPS' XML parsing capabilities are based on eXpat. Although other XML parsing systems are available, they were deemed inappropriate for XPS for technical reasons (Xerces is too big, libxml2 is too hard to comprehend). One of the prime motivators for using eXpat is its speed. It parses XML document very quickly.

Other

As XPS grows there will probably be other external libraries that it uses. We just don't know what they are yet.

XPS Libraries

base

The base library provides fundamental software engineering facilities to XPS such as assertions, error handling, and abstract data types. It is meant to be used as a toolkit from which programs can pick and choose the facilities they need.

cfg

The cfg library provides all compile-time and run-time configuration services. Configuration is handled via a very simple XML file format. This library will grow to deal with all configuration matters, system wide.

meta

The meta library provides the meta-model for XPL and its extensions. This is essentially the high-level IR or abstract syntax tree for XPL based languages.

rt

The rt library provides the runtime library and extensions architecture for the eXtensible Virtual Machine (xvm). This library provides a platform agnostic set of services that may be loaded and executed as intrinsic operations by XPL based programs.

space

The space library manages all aspects of a workspace which is a self-contained repository of code with features for versioning, compilation, promotion, etc.

xml

The xml library provides all XML related services for XPS. This includes parsing, schema and dialect generation, validation of documents, etc.

xpl

The xpl library provides xpl compilation for XPS. It allows XPL programs to be manipulated in a variety of ways.

XPS Tools

XPLC

The xplc tool is the compiler for XPL based languages. It uses the facilities of the xpl library to process XPL programs for the generation of documentation, bytecode, executables, etc.

XVM

The xvm tool is the virtual machine for XPS. It provides a platform neutral low level machine for interpretation and just-in-time compilation of XPL based programs as well as a framework for executing statically compiled programs.

XPSD

The xpsd tool is the XPS daemon. It provides a set of services to network users via an XML-RPC/SOAP based interface. Users can log in, review code, make changes, compile and build programs, promote programs between workspaces, and etc.

XPSH

The xpsh tool is a command line oriented interface to XPS. It communicates with the XPS daemon using a more natural "shell" like interface.