[Insight-developers] MetaIO - versioning

[Bradley Lowekamp]

Hello Stephen,

It sounds quite a reasonable way to move the file format forward. 

My one concern would be testing. All the different versions greatly increase this burden. How to ensure that you can still read the old formats correctly and the newly written old formats are still compatible? Do you have a proposed strategy for testing the different combinations of file formats? 

Brad

On Jan 23, 2011, at 11:59 AM, Stephen Aylward wrote:

> Hi ITK'ers.
> 
> Proposal
> =======
> I am writing to propose adding version information to metaObject
> files, including meta images.
> 
> Problem addressed
> ===============
> Meta was created 14+ years ago and needs updating.   This will allow
> us to better support images of vectors of vectors, spacing per slice,
> ...
> 
> Method
> ======
> We could add a Met_ReadVersion function for meta object developers
> that returns a version number for a file's format.   The version
> number can be read from a file without reading the other contents of a
> file.   MetaObject readers would be able to adjust the fields they
> read from a file based on that version.  MetaObject writers should be
> able to write to older version formats as well as the current version
> format.
> 
> The version tag will be set to 1.0 for all object formats at this
> time.   Thus, if a version number hasn't been specified in the file,
> the MET_ReadVersion function returns 1 (corresponding to the current
> version of meta).   Moving forward, each object can increase its
> version - that is, there will not be a global version number, it will
> be object specific.
> 
> Justification for design: Currently, there is a function
> "Met_ReadForm" that allows a developer to query the type of object in
> a meta file (e.g., image, matrix, arrow, tube,...).    The proposed
> MET_ReadVersion function follows that pattern.
> 
> The file tag will be "ObjectVersion".
> The value of ObjectVersion with be an unsigned int.  (no concept of
> minor/major versioning will be provided).
> -- The tag is ObjectVersion and not FileVersion because the content of
> the file/object will change, not just its organization in the file.
> 
> Comments / suggestions / concerns?
> 
> s
> 
> -- 
> 
> ==============================
> Stephen R. Aylward, Ph.D.
> Director of Medical Imaging Research
> Kitware, Inc. - North Carolina Office
> http://www.kitware.com
> stephen.aylward (Skype)
> (919) 969-6990 x300
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