"Cromwell Enage" <sponage@yahoo.com> wrote: (much snipping throughout)

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Boost.Graph seems to expose and require an unnecessarily large amount of complexity, though.

If by "exposure" you mean lots of source code, I'll take that complexity any day of the week and twice on Sundays. :)

Yes, I should�ve mentioned in my original post that I am unaware of another c++ graph library as powerful and flexible as BGL. It seems peerless at present. I was worried that my queries would be abrasive and am pleased to get such well-written responses.

The library does have a rather steep learning curve, especially if you're somewhat unfamiliar with graph theory and/or template programming.

Perhaps my unrest is an extension of my naivety. We seem to be in agreement about BGL�s complexity, though. I guess the question is whether or not that complexity is absolutely necessary.

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The amount of scaffolding required to use BGL for even the simplest of projects often dwarfs the code size of a naive, yet functional, special-purpose implementation.

Special-purpose implementation of a graph library? Or the project?

Special-purpose implementation of the graph related functions that would otherwise have been provided by a graph library.

Furthermore, while most STL algorithms confine themselves to handling just those STL container elements, most graph algorithms also need the properties of vertices and/or edges as input.

BGL delegates some of the responsibility of

Unquestionably. property

storage to the Boost Property Map Library.

My confusion is as to why managing those properties are left to the client instead of the underlying container. In the case of properties that are intrinsic to the (user-defined) object being stored in the graph, I feel like they should be accessed as attributes of the object and �connected� to algorithms by generally trivial functors. What advantage is had by forcing the client to manage a property map of properties to vertices when they could instead provide a functor to reveal the same information? What about the cases where the needed properties are only relevant to the underlying graph structure and the algorithm, like indices? Wouldn�t it be more elegant to have graph container manage those properties than the client?

Having dwelt in the academic circle known as the University of Central Florida, and thus familiar with the theoretical uses of a graph library (plus I've studied some game development apps on the side), I'd like to learn more about how the Real World would want to use BGL.

I can�t speak for the �Real World� at large, but I can give you an example of the kinds of problems I would typically use a graph library for. When evaluating new programming languages (and often just for fun), I download problem sets from old top-coder and ACM programming contests. In almost every set of problems, there is at least one challenge which would benefit from a standard library graph extension. Usually, they center on things like building conversion equations from a series of ratios, walking a family tree, choosing a good path, scheduling planes, etc � the kind of stuff in an undergrad discreet math class. These problems will almost solve themselves in certain programming languages, but in C++, they require a bit more work (as you know). Doing a few of these problem sets always drives home, to me, the fact that C++ really needs standard facilities for graphs and regular expressions.

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Even knowing that ease-of-use is not a criterion for acceptance into boost, looking at what is required of the client to use the BGL always leaves me feeling perplexed. Is there any particular reason that a simplified interface is not made available?

Again, I don't know a simple graph problem that requires a simplified graph interface.

Simplicity is rarely a requirement as such. Perhaps it is just ignorance on my part, but riddle me this: I can describe a graph in visgraph�s format in a very small number of simple statements, render it, hand it to a person and ask them to answer questions like �is there any path from A to Z?� What fundamental functionality would this kind of simplicity preclude if applied to BGL?

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Perhaps a container adapter could be packaged with the library allowing a compromise of functionality and flexibility for simplicity?

I thought the boost::vector_as_graph class template served that purpose. Wrap it around a std::vector<EdgeList>, with EdgeList = std::list<unsigned int> (or an edge list container of your choice, so long as the value type is usable as an index in the vector), and you should be good to go.

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If a graphing problem is trivial, shouldn't BGL provide a trivial solution? Why are the simplest useful examples several hundred lines of code?

The examples don't seem that big and hard to understand. Of course, quite a few of them have #ifdefs that I could do without since I don't use

This may be an option, although it doesn�t really seem to offer the generational leap in simplicity that I would like. Maybe I am simply needing one more layer of abstraction? Perhaps, I need something that removes the seemingly awkward distinction between the �thing you want to store in the graph� and �the attributes of the thing you want to store in the graph but are not a part of the thing and are instead part of this other thing.� Confusing, isn�t it? the

compilers in question, but I can live with them.

For reference, this is from the Kevin Bacon example: typedef property_map < typedef adjacency_list < vecS, vecS, undirectedS, property < vertex_name_t, std::string >, property < edge_name_t, std::string

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, vertex_name_t >::type actor_name_map_t;

I, personally, would find it much more natural to define an actor type with appropriate members than to manage such declerations. While my views are probably shaped by my limited understanding of the stylistic model, that is one UGLY typedef. It doesn�t really come trippingly off the tongue, does it? The amount of scaffolding required for BGL use is generally large and complex enough that I would find myself writing wrappers for the BGL so that I could use it without constant need for a reference manual. That would generally be a bad situation for me (more work), for other developers (unfamiliar framework dependency), and for end-users (greater risk of bugs via unproven code).

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I apologize for all of my vague criticisms - my intention is not to flame but rather to test the waters.

Your criticisms seem healthy, and I hope my responses are helpful.

Thanks ever so much. I guess that all I have to worry about now is making a fool of myself.

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It is difficult for me to assess whether the simplicity I yearn for isn't present for stylistic reasons or whether it would rather necessitate a sacrifice of flexibility, functionality or implementation clarity. Nor is it clear to me to what extent these criteria can be compromised to promote clarity of client code. For what it is worth, the kind of ease-of-use I'm imagining might look like:

#include <less_than_10_graph_headers> ... digraph<some_node_type,some_edge_context_type> g; g << "vertex" << make_pair("vertex", "implicit_vertex"); g.add_edge("brother", "sister", "sibling"); if(g.find(make_pair("brother", "sister"))) related = true;

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Could someone please elucidate on why it is impossible/impractical/unnecessary/whatever for a graph library to have such an interface?

I believe the potential for ambiguity would hinder this syntax the most. In this case, you'd have to overload operator<< to input both edges and vertices,

You are absolutely correct. I should�ve been more careful in presentation. Using operator<< in this case was probably a poor choice, anyway. Using add_* would�ve conveyed more information.

and what if some_node_type turned out to be std::pair? You couldn't pass in make_pair(vertex,vertex) as an edge then.

I believe that would be ambiguous only if a vertex was somehow illegally defined to be a pair of vertices. Regardless, g.add_edge(x,x,x) is just as simple to type.

The same goes for g.find(); is it supposed to find a vertex, an edge, or both?

find would�ve been much more descriptive written as std::find(g.dfs_begin(�brother�), g.dfs_end(), �sister�) or some such. These are just ideas, of course, not proven interfaces. And my illustration wasn�t really intended so much as an example of syntax as an example of what I considered to be a �friendly� api.

Also, it seems you want to be able to use non-built-in or custom types as vertex IDs.

You'll have to build your own custom-type-to-vertex map and bind it to

Actually, I would prefer to use non-built-in types as the vertex. If additional meta-data is needed for internal maintenance, then I don�t generally want to be bothered/privileged with it as a client. the

graph;

It seems like that would be better left to the framework.

BGL won't do it for you, to retain its genericity.

It seems like adding another layer of abstraction should decrease coupling instead of adding it. I don�t really see how specifying that I want a graph of file dependencies, for example, is any less generic than saying that I want a graph of property maps where the id is a filename. Regards, prs __________________________________ Do you Yahoo!? Yahoo! Small Business $15K Web Design Giveaway http://promotions.yahoo.com/design_giveaway/