The IFC Building Model: A Look Under the Hood

[beegee]

An Article worth the read....

What exactly is the IFC (Industry Foundation Classes)? Most professionals simply know of it as a data model developed by the IAI (International Alliance for Interoperability) to facilitate interoperability in the building industry. While technical information about the IFC building model is documented in detail and is readily available for software developers who need to work with it, there is practically no information for the average AEC practitioner who wants to have a better understanding of the IFC model. The intent of this article is to address this shortfall. It is not about interoperability or data integration per se; rather, it is focused on providing a broad overview of the IFC model without delving too deeply into its technicalities.

[Wes Macaulay]

Whenever I think about one of these platform independent schemas I imagine how much work it must take to make it work. And the file size: unless there's some sort of compression or binary (non ASCII) method of storing the IFC/STEP/whatever data, you'd think the file would have to be huge! It's still an important task that all the CAD vendors should perform; that way my Revit building can be analysed in 3D by someone's structural modelling app and someone else's energy loss app, etc.

[bclarch]

I agree Wes. It looks to be a total can of worms once you start considering all that is involved. I can't see every piece of CAD software working with the same native data format. I think that best that we can hope for is an intelligent target standard (similar to the function that DXF serves in the 2D market) which every 3D software can export to and import from. Even then, there are always going to be translation issues. It is, however, a nice goal to shoot for. I hope that all of the software players get onboard.

[Scott D Davis]

Isn't ODBC an open format? Can't any database program read an ODBC compliant file? Answered my own questions with a quick google:

From http://www.webopedia.com/TERM/O/ODBC.html

ODBC: Short for Open DataBase Connectivity, a standard database access method developed by Microsoft Corporation. The goal of ODBC is to make it possible to access any data from any application, regardless of which database management system (DBMS) is handling the data. ODBC manages this by inserting a middle layer, called a database driver , between an application and the DBMS. The purpose of this layer is to translate the application's data queries into commands that the DBMS understands. For this to work, both the application and the DBMS must be ODBC-compliant -- that is, the application must be capable of issuing ODBC commands and the DBMS must be capable of responding to them. Since version 2.0, the standard supports SAG SQL.

With this in mind, it seems that the IFC should work towards using this as a standard, rather thatn once again creating ANOTHER file format and trying to make it a 'standard'

[aaronrumple]

XML

That get's my vote.

[GuyR]

Isn't ODBC an open format?

Don't think it's open as in Opensource. It's also just a means for extracting data from a relational database on the windows platform. It's not a storage format.

Please revit team correct me if I'm wrong but the question is, is a relational database a good way to store a building model? My nderstanding is revit isn't a relational database more an object database like IFC. For instance how would you store a spline and a line in a relational DB. A line can be stored as 4 fields (x1,y1,x2,y2), a spline? So a relational model would require 2 tables to store these 2 elements.An object DB would store each as say a lineElement with the appropriate definition subclassing this.

IFC success is very dependent on Autodesk supporting the standard. ADT development of IFC is carried out by a German company not head office now. There has been talk about Revit supporting IFC. The question much like with API's is when.

XML,That get's my vote

There is a variant of the binary IFC called ifcXML.

Guy

[Scott D Davis]

There is a variant of the binary IFC called ifcXML.

Maybe we are seeing the beginning of this with the gbXML in 6.1.

[GuyR]

Maybe we are seeing the beginning of this with the gbXML in 6.1.

Yep, I think gbXML was based on the ifcXML schema. From the gbXML schema changelog:

2/12/01
Changing from X3D elements to ifcXML elements.

So hopefully this is the start.

Guy

[hand471037]

I would love to see some level of IFCxml done in Revit, if only to shut up the ArchiCAD people about how Revit doesn't have it.

Serously tho, it would be great, however the IFC format is kinda twisted from what I understand, there are different values (like 1.1, 2.0, 2.?) that don't talk directly with each other, and certain products (like timberline) will use one and not the others.

I see much more value in IFC Xml, for then it would be easy for non-programmers to pick through the export data and write tools for doing neat things with it. I'vee been looking at the gbXML files, and wondering what I could do with that info...

Also, on ODBC, it's not open, but it can talk to open standard databases. It's more a 'conduit' than anything, so you could choose to have it communicate with an open source database IIRC and then be 'open'.

[FK]

Please revit team correct me if I'm wrong but the question is, is a relational database a good way to store a building model?

A pure relational database, hideous. Object-relational (i.e., everything on the market), maybe. Pure object-oriented, good.

Graphics/CAD are particularly suited to object-oriented data modeling. Translating these models into relational schemas is possible, but error-prone and painful. For example, inheritance is a pain to set up in a pure relational database. Note that you can always write an ODBC driver that would take SQL queries and omit all the object-oriented complexity.

XML is actually a hierarchical model.