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Maintained by Andrew McCallum <mccallum@gnu.ai.mit.edu>, with contributions by Pascal Forget <pascal@wsc.com>, Scott Christley <scottc@net-community.com>, and Randy Chapman <chapman@u.washington.edu>. Last updated 26 March 1996. The most up-to-date version of this FAQ is available at `ftp://ftp.cs.rochester.edu/pub/u/mccallum/gnustep-base'. Please send corrections to <mccallum@gnu.ai.mit.edu>. The intended audience of this FAQ is future and present code developers for GNUstep. This FAQ serves a purpose complementary to the GNUstep WWW pages--since it is written and maintained directly by those writing code for GNUstep, it emphasizes (although not exclusively): (1) technical details and organization, (2) the functionality is coded and working now. This FAQ is intended to provide a succinct document in which to find GNUstep information without hype. GNUstep General Information =========================== 1. What is GNUstep? GNUstep is the Free Software Foundation's effort to implement NeXT Software Inc.'s OpenStep Standard. The project is not finished, however some components are useable now. The GNUstep project consists of the following sub-projects: * GNU Objective C Compiler and Objective C Runtime Library - Although not actually a sub-project the GNUstep, GCC and the GNU Objective C Runtime Library are integral to GNUstep, since they are used to make every GNU Objective C program. * GNUstep Base Library - Code for non-graphical objects, such as strings, collections, archiving support and distributed objects messaging. (Including functionality similar to OpenStep's `FoundationKit'.) * GNUstep GUI Library - Code for graphical objects used in making a Graphical User Interface (GUI). This includes buttons, sliders, text fields, windows, menus, etc. (Including functionality similar to OpenStep's `AppKit'.) * GNUstep DisplayGhostScript Server - A server that draws PostScript graphics to the screen, and receives events from the keyboard and mouse. It is based on GhostScript. * GNUstep Interface Modeller Application - An application for graphically assembling application interfaces. More detailed information about each of these sub-projects can be found in their own sections below. There are several projects related to GNUstep that are not officially part of the GNU project and GNUstep, but may become so in the future. These include: the `G3DKit' project, (contact Thomas Engle <tsengel@cip.informatik.uni-erlangen.de>); an application library based on OpenGL, (contact Georg Tuparev <Tuparev@EMBL-Heidelberg.de>); and `ProjectCenter', a source code management and development environment, (contact unknown). If you know of others, please contact the FAQ maintainer. The initial target platforms for GNUstep are Linux and other UN*X's. There has been some OS/2 WARP work, but I have not seen any ongoing work on this platform yet, (contact McCallum if you are interested). 2. What is the OpenStep standard? OpenStep is an Application Programming Interface (API) for creating applications using the Objective C language. It was published by NeXT Computer Inc. in 1994. OpenStep consists of three parts: the `FoundationKit', a library of non-graphical objects; the `AppKit', a library of objects usful in creating graphical applications; and `DisplayPostscript', an interface for drawing to the screen using the PostScript graphics language. You can obtain a copy of the OpenStep standard in * texinfo at `http://www.dartmouth.edu/~ajones/Projects'. * HTML at `http://www.nmr.embl-heidelberg.de/GNUstep/GNUOpenStep'. * PostScript and RTF at `ftp://ftp.next.com/pub/OpenStepSpec/'. 3. Who is currently involved in writing GNUstep code? For the sake of being social and getting to know each other, here is a list of the folks who are currently, actively contributing GNUstep code. The list includes a brief descriptions of each person's background and involvement in the GNUstep coding efforts. * Adam Fedor <fedor@mode.colorado.edu> continues his excellent, long service as user, tester, and code contributor to both the Base Library and the GUI Library. * Andrew McCallum <mccallum@gnu.ai.mit.edu> was appointed chief maintainer of the GNUstep project by Richard Stallman in January 1996. He has been involved and hacking in the NeXT community since NeXTSTEP version 0.8; he has been working on GNU Objective C and the Base Library since 1993. * Pascal Forget <pascal@wsc.com> is working on the GUI Library in conjunction with Scott Christley. He has worked with Randy Chapman's DisplayGhostScript and X Windows as a GNUstep GUI backend. * Randy Chapman <chapman@u.washington.edu> has been working on the GNUstep DisplayGhostScript Server, adding DPS extensions to GhostScript, including pswrap work. * Scott Christley <scottc@net-community.com> is in charge of the InterfaceModeler project, which is currently in the design stages. He is working on the GUI Library in conjunction with Pascal Forget. He has already written much of the GUI Library frontend. There are many others who have made significant contributions to GNUstep, but who are not currently contributing code, (such as Kresten Thorup <krab@next.com> and Paul Kunz <paul_kunz@slac.stanford.edu>). For more information about GNUstep history, see the GNUstep WWW pages. There are also several others who have contributed individual classes to GNUstep, but who are not actively contributing to general GNUstep work. This list is not intended to be a complete list of GNUstep code contributors; that information is available in each of the GNUstep code packages. There are also other code developers who are writing Objective C code related to GNUstep, but for projects that are not officially part of the GNU project and GNUstep. We hope that some of these projects will join the GNU project and GNUstep in the future. Please send corrections to the FAQ maintainer. 4. Is there a WWW site for GNUstep? Are there mailing lists for GNUstep? There is a WWW site at `http://www.GNUstep.org', (and its mirror `http://www.NMR.EMBL-Heidelberg.DE/GNUstep', that contains many useful pointers. The technical information in this FAQ may be more up to date than the WWW pages since this FAQ is maintained directly by the people who are developing GNUstep code. There are several mailing lists: * <discussion@gnustep.org> is a mailing list for general discussion of GNUstep developments. Announcements about GNUstep progress are also made there. The list is maintained by Georg Tuparev <Tuparev@EMBL-Heidelberg.de>. To join, send mail to <discussion-request@gnustep.org>. * <webmasters@gnustep.org> is a mailing list for discussion of the GNUstep WWW site. To join, send mail to <webmasters-request@gnustep.org>. * <g3dkit@gnustep.org> is a mailing list for discussion of a library for drawing 3D graphics; it is based on OpenGL and RenderMan. The Free Software Foundation is hoping that this work can become an official part of the GNU project and the GNUstep project. To join, send mail to <g3dkit@gnustep.org>. * There is also a private mailing list for the core active developers of GNUstep. Those people who contribute large sections of code and who are interested in making and planning further contributions may be invited to join. We apologize in advance, but, for the sake of efficient communication, the list is not open to people who are not actively contributing significant coding work to the project; don't bother asking to be added unless you have already been in contact with Andrew McCallum about source code contributions. If you would like to make code contributions, by all means, contact McCallum. This list is maintained by McCallum <mccallum@gnu.ai.mit.edu>. 5. What is the current state of the project? When can I expect it to be completed? The Base Library is about 85 percent done. Significant useful work can already be done using the library. The GUI library is about 25 percent done. It is going through a major transition at the moment to coordinate work from multiple developers, DisplayPostscript, and the non-OpenStep objcX library into a single package that will be made available to the public. The DisplayPostscript and drawing support is also in transition. More detailed information about the state of each of the sub-projects can be found below. With free software, you should never, ever, believe promises about when a project will be finished. ...However, that said: there are certain GNUstep developers that are counting on having useful Base and GUI libraries working by the end of Summer 1996. 6. On what platforms will it run? The short answer is: On whichever platforms volunteers offer port it! The main target platforms is free operating systems, namely Linux and the Hurd. Much of the code is OS-independent, and should port quite easily to various UNIX-like OS's. There has been interest in a port to Linux on the Apple Macintosh, but I have not heard of any developers. At least one of the current active developers is also working with WindowsNT. There has been some interest in an OS/2 port, but I've seen few code contributions for OS/2. 7. How can I help? If you have a specific piece of functionality that you would like to contribute, or if you would like to ask for suggestions about what coding work you can do to help, contact the GNUstep Chief Maintainer, Andrew McCallum <mccallum@gnu.ai.mit.edu>. More detailed inforation about each of the GNUstep sub-projects can be found below. GNU Objective C Compiler and Objective C Runtime Library ======================================================== 1. What is the Objective C Runtime Library? The Objective C Runtime Library provides C functions and data structures required to execute an Objective C program. An introduction to the Objective C Language is provided at `http://www.next.com/Pubs/Documents/OPENSTEP/ObjectiveC/objctoc.htm'. The Frequently Asked Questions list for `news://comp.lang.objective-c' can be found at `??'. The GNU Objective C Runtime Library offers everything NeXT's runtime does, including Categories, Protocols, `+poseAs:', thread-safety, class initialization on demand, delayed loading of classes, and initialization of static instances (such as @""-style string objects). It also has several improvements over NeXT's implementation: * NeXT's runtime requires an extra function call (objc_msgSend) for each message that is sent; (the function looks up the receiving instance's implementation of the method). GNU's implementation is faster because it does not use an extra function call. Instead, it inlines a short piece of code that makes two pointer hops into a method dispatch table; because the code is inlined, it does not incur the overhead of a function call. * When running in thread-safe mode, NeXT's runtime must aquire a global mutual exclusion lock every time a message is sent; this is extremely slow. GNU's runtime, amazingly, sends messages just as fast in thread-safe mode as it does in single-thread mode--the code path does not contain even a single extra instruction! The GNU runtime only needs locks when certainly structures are written, not read; the structures are written relatively infrequently: only at class initialization and when `+poseAs:' is called. * GNU's runtime provides "selector-types" along with each selector; NeXT's does not. A selector-type is a string that describes the C variable types for the method's return and argument values. Among other uses, selector-types is extrememly helpful for fast distributed objects implementations, (see GNUstep Base Library Section, below). * Many of the GNU functions have different names than their corresponding NeXT functions; the GNU names conform to the GNU coding standards. * GNU's runtime library has a new class heirarchy manipulating method called `-transmuteClassTo:'. It can change the class of an instance to a cousin class of the same instance-size. * NeXT's compiler, `cc', is based on an old version of `gcc'. GNU's compiler is, of course, the latest version of `gcc', and therefore contains all the latest enhancements. 2. What is its current state of development? GNU's Objective C Runtime library has been stable and useable since 1993. Enhancements continue to be made. GCC contains the source for the GNU Objective C compiler and runtime library. It can be obtained from `ftp://prep.ai.mit.edu/pub/gnu', or any other mirror of the GNU archives. As far as I know, the GNU Objective C Runtime runs on all, platforms on which GCC runs. GCC version 2.7.2 does not contain the thread-safe features, but the next version of GCC will. A patch for thread-safe features is provided with the latest developer snaphots of the GNUstep Base Library. There are currently thread-safe backends for DEC OSF/1, Solaris, IRIX, and WindowsNT. Volunteers are solicited for writing additional back-ends, especially one for Linux. GNUstep Base Library ==================== 1. What is the GNUstep Base Library? The GNUstep Base Library is a library of general-purpose, non-graphical Objective C objects. For example, it includes classes for strings, collections, byte streams, typed coders, invocations, notifications, notification dispatchers, times, network ports, remote object messaging support, event loops and random number generators. It provides functionality that aims to implement the `FoundationKit' portion of the OpenStep standard. In many cases, the `NS*' classes are implemented as wrappers around more featureful GNU classes. There is more (although perhaps out-of-date) information available at the GNUstep Base Library homepage at `http://www.cs.rochester.edu/u/mccallum/gnustep-base'. 2. What is its current state of development? It is about 85 percent of the way to having all the OpenStep classes. Significant useful work can already be done using the library since the missing 15 percent are the less-often-used classes, such as NSByteStore. Over 60,000 lines of code have already been written. The following OpenStep classes and class clusters are pretty much done and usable: NSArchiver, NSArray, NSAssertionHandler, NSAutoreleasePool, NSBitmapCharSet, NSBundle, NSCharacterSet, NSCoder, NSCountedSet, NSData, NSDate, NSDictionary, NSEnumerator, NSException, NSInvocation, NSLock, NSMethodSignature, NSNotification, NSNotificationCenter, NSNumber, NSObject, NSProcessInfo, NSRunLoop, NSSet, NSString, NSThread, NSTimeZone, NSTimer, NSValue. Most of the C functions are also implemented, including NSHashTable and NSMaptable. A GNU implementation of Distributed Object works. However, the wrappers for creating the NSConnection, NSDistantObject, NSProxy wrappers have not yet been made. The following classes are unstarted or unusable: NSBTreeBlock, NSBTreeCursor, NSByteStore, NSByteStoreFile, NSCalendarDate, NSDeserializer, NSScanner, NSSerializer, NSUserDefaults. 3. In what ways is the Base Library different from OpenStep's FoundationKit? It contains several enhancements: 1. OpenStep has a single NSInvocation class, which is based on sending a message to an object. The GNUstep Base Library has a heirarchy of Invocation classes with various capabilities. Two of the Invocation subclasses can cause C functions to be called, instead of sending messages to objects; these subclasses are useful when one would otherwise have to write a new class and method to implement some simple, stateless functionality. Other subclasses of Invocation could hold GUILE or TCL code to be run, or could record their invocation information to a file. All of them respond to a new method called `-invokeWithObject:' that is useful for enumerations. 2. I have been told that OpenStep's NSNotificationCenter is slow. GNUstep's NotificationDispatcher class is based on interesting use of linked lists and hash tables in such a way that it should be comparatively very fast. OpenStep notifications must be method selectors sent to objects. GNUstep notifications can invoke an Invocation instead, thus taking advantage of the flexbility and context-holding capability of Invocation objects. 3. OpenStep takes a disconnected "class forest" approach to collection classes. GNUstep has all the OpenStep collection classes, however they are build from underlying GNU collection classes that are organized as a deep class heirarchy. Because of the deep heirarchy, there is a built-in uniformity of method names, and there are common abstract superclasses in which to add new common functionality. Unlike OpenStep, the Base Library also has additional collection classes for heaps, stacks, queues, trees and linked lists. There is also a rich variety of enumeration methods based on invocations. 4. OpenStep's archiving mechanism provides only one choice of backend format. By backend format, I mean a format for writing C types, such as ints, floats and C strings. The GNUstep archiving mechanism has a clear separation between frontend and backend. Different backends are provided. One backend writes in human-readable and human-editable ASCII text, (including programmer-provided text name labels for each of the items.) Another writes in a compact, stream machine-independent bits. A third writes in an even more compact stream of machine-dependent bits; this is useful for distributed objects connections on machines of the same architecture. I'm not sure how OpenStep's archiving system implements forward references, (that is, calls to `encodeConditionalObject:' for which the object argument has not yet been encoded, but will be encoded later.) According to its restricted interface, NeXT's implementation must either (1) make two passes through all the -encodeWithCoder: methods of the objects to be encoded, or (2) not handle forward references with `-encodeConditionalObject:', only backward references. GNU's archiving system, on the other hand, implements forward references efficiently, without making two passes. It does this by using an object decoding method (`-decodeObjectAt:..') that back-patches `id'-pointers when the conditionally encoded objects are found in the coded stream. 5. OpenStep's distributed objects mechanism requires four network "hops" when sending and responding to each new method--one to send the request, one for the server to request the method type from the client, one for the client to respond with the method type, and one to respond with the return value of the method call. GNUstep distributed objects takes advantage of the superior GNU Objective C runtime, which includes the method type locally with the selector. Since the method type can already be found on the server, there is no need to ask the client for the type, and GNU distributed objects takes two less network hops. 6. NeXT's Objective C runtime becomes very slow when thread-safety is turned on since the runtime must acquire a global mutual-exclusion lock each time an Objective C message is sent. GNUstep takes advantage of the superior GNU Objective C runtime, which is requires zero extra time to send a message when thread safe--not even one instruction more is required for a thread-safe message send. Mutual exclusion locks are only necessary in the relatively infrequent times in which classes are initialized or `+poseAs:' is called. Galen Hunt implemented the patches to make the runtime thread-safe. 4. What are the features of GNU Distributed Objects? GNU Distributed Objects has many of the features of other distributed objects implementations, but, since it is free software, it can be ported to platforms for which other distributed objects implementations are not available. If you are interested in having it ported to a new platform, or if you have any questions about it, please contact Andrew McCallum, <mccallum@gnu.ai.mit.edu>. The distributed object support classes are Connection, Proxy, ConnectedCoder, Port, TcpPort, UdpPort, and MachPort. Of the various Port backend's, currently only the the TcpPort is in working order. [NOTE: The GNU distributed object facilities have the same ease-of-use as NeXT's; be warned, however, that they are not compatible with each other. They have different class heirarchies, different instance variables, different method names, different implementation strategies and different network message formats. You cannot communicate with a NeXT NXConnection using a GNU Connection. Here are some differences between GNU distributed objects and NeXT's distributed objects: NXConnection creates NXProxy objects for local objects as well as remote objects; GNU Connection doesn't need and doesn't create proxies for local objects. NXProxy asks it's remote target for the method encoding types and caches the results; GNU Proxy gets the types directly from the local GNU "typed selector" mechanism and has no need for querying the remote target or caching encoding types. The NXProxy for the remote root object always has name 0 and, once set, you cannot change the root object of a NXConnection; the GNU Proxy for the remote root object has a target address value just like all other Proxy's, and you can change the root object as many times as you like. See the "lacking-capabilities" list below for a partial list of things that NXConnection can do that GNU Connection cannot.] Here is a partial list of what the current distributed objects system can do: * It can pass and return all simple C types, including char*, float and double, both by value and by reference. * It can pass structures by value and by reference, return structures by reference. The structures can contain arrays. * It obeys all the type qualifiers: oneway, in, out, inout, const. * It can pass and return objects, either bycopy or with proxies. An object encoded multiple times in a single message is properly decoded on the other side. * Proxies to remote objects are automatically created as they are returned. Proxies passed back where they came from are decoded as the correct local object. * It can wait for an incoming message and timeout after a specified period. * A server can handle multiple clients. * The server will ask its delegate before making new connections. * The server can make call-back requests of the client, and keep it all straight even when the server has multiple clients. * A client will automatically form a connection to another client if an object from the other client is vended to it. (i.e. Always make a direct connection rather than forwarding messages twice, once into the server, from there out to the other client.) * Servers and clients can detect port deaths (due to remote application crash, for example) and close down gracefully, announcing the closed connection to other objects who have requested notifications. * Exceptions that occur in the server (during the course of servicing a request) are sent back to the client, and the exception is then properly raised in the client's process. * Servers and clients can be on different machines of different architectures; byte-order and all other architecture-dependent nits are taken care of for you. You can have SPARC, i386, m68k, and MIPS--Linux, SunOS, Solaris, IRIX, AIX and HPUX machines all distributed-object'ing away together in one big web of client-server connections! The library can be ported to other architectures and operating systems also. Please contact Andrew McCallum, <mccallum@gnu.ai.mit.edu>, if you are interested in having a new port of GNU Distributed Objects. Here is a partial list of what the current distributed objects system does not yet do: * Run multi-threaded. * Return structures by value. * Use Mach ports, pass Mach ports, pass Mach virtual memory. 5. What is the general organization of the non-OpenStep, GNU classes? (This FAQ does not describe the OpenStep standard classes, because a detailed description of those can be found in the OpenStep documentation.) Here are some of the public GNU classes. See the source header files for more information. The collection class heirarchy: ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Collection Root all the collection classes (abstract) Set Unordered collection, no duplicates Bag Unordered collection, may have duplicates KeyedCollection Contents accessible by object key (abstract) Dictionary Concrete implementation MappedCollection One collection maps into another IndexedCollection Contents accessible by integer (abstract) BinaryTree Basic, sorted binary tree RBTree Red-Black tree, sorted, more balanced SplayTree Splay operation keeps tree balanced OrderedCollection Can insert at arbitrary index (abstract) Array Basic array Queue First in, first out Stack First in, last out GapArray Efficient handle middle insert and delete LinkedList More efficient than arrays for some ops Strings (as in Smalltalk, part of the collection class heirarchy): ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ConstantString Root of string classes, chars not changable String contents can be changed *CString Strings based on 1-byte characters Writing/reading bytes, C-type variables, and connected groups of objects: ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Stream Source and Destination for stream of bytes StdioStream Stream based on FILE* (files, pipes, etc) MemoryStream Stream based on memory buffer CStream Write/Read C-type variables on stream TextCStream use human-readable format BinaryCStream use compact machine independent format RawCStream use even more compact machine depedent format Coder Write/Read groups of objects on CStream Encoder Writing Archiver for files ConnectedEncoder for distributed objects Decoder Reading Unarchiver for files ConnectedDecoder for distributed objects Holding code to be run on request: ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Invocation Contains code that can be run ArgframeInvocation based on gcc __builtin_apply() MethodInvocation invokes a method on an object ObjectMethodInvocation the method takes at least one object arg ObjectFunctionInvocation calls a function with type (id(*)(id)) VoidFunctionInvocation calls a functions with type (void(*)()) Posting information about happenings: ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Notification for posting information others may want NotificationRequest a record of an observers request NotificationInvocation will be posted by invoking an Invocation NotificationPerformer will be posted by -perform:withObject NotificationDispatcher distributes Notification's among requestors Distributed Objects Support: ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Connection between two machines on which messages sent Proxy Representative of a remote object Port A mailbox for packets InPort for receiving packets OutPort for sending packets Tcp*Port based on TCP/IP Udp*Port based on UDP/IP Mach*Port based on Mach ports Packet holds data and reply port 6. Where can I get a copy? The most recently released "official" version can be obtained from `ftp://prep.ai.mit.edu'. The most recently released alpha version can be obtained from `ftp://alpha.gnu.ai.mit.edu'. The most recent developer's snapshot can be obtained from `ftp://ftp.cs.rochester.edu/pub/u/mccallum/gnustep-base'. These releases are there for exchange between active GNUstep coders, and for curious code-readers, not for naive users; read the README.first file in the FTP directory. GNUstep GUI Library =================== 1. What is the GUI Library? The GNUstep GUI Library is a library of objects useful for writing graphical applications. For example, it includes classes for drawing and manipulating graphics objects on the screen: windows, menus, buttons, sliders, text fields, and events. There are also many peripheral classes that offer operating-system-independent interfaces to images, cursors, colors, fonts, pasteboards, printing. There are also workspace support classes such as data links, open/save panels, context-dependent help, spell checking. It provides functionality that aims to implement the `AppKit' portion of the OpenStep standard. However the implementation has been written to take advantage of GNUstep enhancements wherever possible. 2. Explain the organization of the front- and back-ends. The GNUstep GUI Library is divided into a front- and back-end. The front-end contains the majority of implementation, but leaves out the low-level drawing and event code. A back-end can override whatever methods necessary in order to implement low-level drawing event receiving. Different back-ends will make GNUstep available on various platforms. The default GNU back-end will run on top of X Windows and the DisplayGhostScript Server. Other back-ends could allow GNUstep to run on OpenGL, OS/2, and WIN32 graphics/event platforms. Much work will be saved by this clean separation between front- and back-end, because it allows different platforms to share the large amount of front-end code. The front-end does not specify what mechanism to use in order to "plug in" the back-end--that is the back-end implementor's choice. At least two backends will use `+poseAs:' method, for example, running `[XDPSWindow poseAs: [NSWindow class]]'. Using `+poseAs:' is more flexible than using Categories because it allows the the back-end implementor to choose what to override in the front-end, instead of having the interface between front- and back-end fixed by the front-end. 3. What is the current state of development of the front-end? A number of classes in the front-end are complete or almost complete; these include: NSActionCell, NSButtonCell, NSButton, NSCell, NSControl, NSEvent, NSFont, NSResponder, and NSSlider. Other classes are complete enough to use, but still require some major additions before being considered almost complete: NSApplication, NSBox, NSColor, NSFontManager, NSMenu, NSMenuCell, NSPopUpButton, NSSliderCell, NSText, NSTextField, NSTextFieldCell, NSView, and NSWindow. All remaining classes have stub implementations. 4. What is the current state of development of the X/DPS back-end? 5. Where can I get a copy? It is not yet publically available. When it is available you will be able to find it in `ftp://alpha.gnu.ai.mit.edu/gnu'. GNUstep DisplayGhostScript Server ================================= 1. What is the DisplayGhostScript Server? 2. What is its current state of development? 3. What is the relationship between the DisplayGhostScript Server and X Windows? GNUstep Interface Modeller Application ====================================== 1. What is the Interface Modeller? Interface Modeller, in its simplest form, is an application for visually constructing and prototyping graphical user interfaces. At a more abstract level, it is a tool for connecting instances of Objective C classes to create a graph of objects; this graph is a model of an executable program that Interface Modeller can save to a file to be loaded and executed later outside of Interface Modeller. 2. What is its current state of development? It is in the specification stage; no code has been written yet. The current specifications are available through the GNUstep WWW pages. All trademarks mentioned on in this FAQ belong to their owners.