XMP files?

Aperture won't be able to read any image adjustments in the XMP files. There is no standard format for adjustments in XMP files. It's possible that these adjustments were made in Lightroom, in which case it may be able to read this proprietary data. But Aperture won't be able to do so.

Aperture will pick up any keywords in the files, and may pick up ratings and keywords. But it will not pick up adjustments.

It's possible that these adjustments were made in Lightroom, in which case it may be able to read this proprietary data.

Not only just for Photoshop Lightroom by or in itself for it's own propriety info, it is also useable with Photoshop CS5 and some other image editing apps that understand XMP data. If I recall that, a couple years ago, Adobe and few other software development companies including Microsoft and possibly Apple had a group of software engineers discussed on the topic. But at the moment, I could not find the source of info that mentioned this now. However, I remember this that it had been discussed a couple years ago. It is possible that Adobe probably have a link to that somewhere at Adobe website for that matter.

In closing, XMP Metadata is a set of standardized information about a photo, such as the author’s name, resolution, color space, copyright, and keywords applied to it. Perhaps it is well worth to do a research on it and get most out of it on your own.

Perhaps that someone could chime in and correct the unbiased info better than I do.

Hope that helps.
Brian

XMP stands for eXtensible Metadata Platform. It is an XML file, and you can slap anything in there you want. Keywords, adjustment metadata, etc. That Adobe is putting adjustment info in there doesn't necessarily mean it's "standard," though. It's just that various Adobe products can interpret that info. But other products from other manufacturers cannot, Aperture included.

One simple example: Lightroom and Aperture handle their brushes completely differently. Aperture uses masks that it saves as TIFF files which are used to mask adjustments. Adobe records them all in the database and can save this out in the XMP file.

So some of the data in the XMP file is "standardized" (mostly the IPTC info), and it's also possible to write non-standardized data in there as well. A "well behaved" application will just ignore information that it doesn't understand (as opposed to, say, crashing), and given an XMP file is actually in XML format this is fairly straightforward.

Yup - what William and Caramel said. XMP files are sometimes referred to as "sidecar" files. One of the main uses for them in AP and LR is for the non-destructive editing capabilities. When you tell AP or LR what kind of adjustments to make to an image, it doesn't actually change the file itself...it does kind of a "note to self" thing and writes a record of changes into the XMP file. If those get separated from the underlying JPEG or RAW file, then you might lose your record of the edits, but the file isn't changed.