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Mess of Metadata


© May 2019 Anthony Lawrence

There was a long series of comments at the article about mdfind that got very confused talking about OS X metadata. I thought I'd try to straighten some of that out in a separate post - though honestly I'm still easily confused myself!

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First, what metadata are we talking about? For an old Unix hand, the metadata is information stored in the inode: file size, permissions, pointers to datablocks, link counts.. that's traditional metadata.

However, there's more metadata today - not just in Unix systems, but especially in Mac OS X. There are extended permissions, acl's, xattributes, Spotlight related metadata.. it's very hard to ferret all this out of Google because similar terms are used for dissimilar features.

Macs had 'resource forks' early on. OS X still has resource forks. but apparently Apple would like to move away from those. That's probably why things get so darn confusing: search for information on metadata and OS X and you'll find lots of pointers to things that talk about resource forks, but usually that's deprecated and doesn't usually apply to OS X.

Let's take Spotlight metadata first. These are specific keys that Spotlight indexes. For example, you can do things like this:

How does Spotlight get the info to index? It asks an Spotlight Importer. This BASICS OF SPOTLIGHT page explains:

Once the Mac OS does kick-off the extraction of metadata from a file, it does so through a Spotlight Importer. Spotlight Importers are plug-ins for the Mac OS that a developer provides specifically for helping files created by their applications to be searchable within Spotlight. Spotlight crawls through its list of changed files, handing each one to the appropriate importer. The importers then read the files, compile a list of metadata, and then hand the metadata back to Spotlight. At this point, the changed file is available for searching within Spotlight.

OK, great, but where does the metadata that the importer supplies come from? Apparently, that's up to the developer. Apple's Extracting Metadata from Documents says:

Avoid the use of external files to store metadata content. All critical metadata should be in the same file as the data. The system store of metadata should be considered volatile.

I want to quibble a little: if it's stored in the data file, it's really not metadata, is it? But never mind. Some apps do it that way. For example, ID3 tags. But other apps do not. For example. In my ~/Library/Caches/Metadata I found some interesting stuff. *Some* apps store Spotlight metadata there. I found:

If I look in Billings, I find this:

But obviously not all apps store their Spotlight related metadata there. Entourage does, as seen in this HOW DOES ENTOURAGE WORK WITH SPOTLIGHT? bit:

When you enable Spotlight indexing within Entourage, a 'cache' file is created for each item within your Entourage database. If you have 100,000 e-mail messages in your Entourage database, 100,000 cache files will be created. If you want to see the cache files, you can find them within your Library/Caches/Metadata/Microsoft folder.
Each cache file contains all the metadata that will be needed for indexing by Spotlight. All changes within Entourage are reflected to the cache files. Create a new item and a new cache file will be created. Updated an item and its cache file will update. Delete an item and its cache file will be deleted. With all these changes, Spotlight receives file change notifications and eventually will ask the modified cache files to go through the import process using the Entourage Spotlight Importer.

But there's no iTunes folder there..

There are also defaults. If I create a text file with 'date > file', an 'mdls' will show Spotlight keys:

Obviously the 'date' command didn't create those. Spotlight won't even index that file (no extension), but it has some default keys just the same! See Spotlight, mdfind (Mac OS X Tiger searching) for more on that.

You can add metadata yourself and can modify one item of Spotlight's domain.

The only Spotlight related data you can modify is kMDItemFinderComment. You do that with GetInfo and after adding it, xattr shows this:

Note that this gives us the clue as to where the data was stored, but I don't find a file with that 'com.apple.metadata' name. I do find:

But those aren't related.

So what do we know? Well, we know it's up to the application responsible for a file to provide importer code. It's up to the same app to decide where to store metadata. Obviously, that implies that for some data that would be the across all files of this type, there's no need to store it anywhere - the importer could generate the response when Spotlight asks.

That's as far as I've gone.. maybe someone else can add more.


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2020-12-28 17:33:50 • Filed to: macOS 10.14 Solutions • Proven solutions

To peruse and interact with files more rigorously, it’s imperative for Mac users to know how to access and manipulate the metadata of files. The metadata of a file is a corpus of data originating from the tagging operations of the OS that ensue when you save files to local folder on your Mac. It includes the background information about the file which provide sorting functions with cues to trace out the file’s location.

It’s a cake walk to view metadata in the Mac OS Mojave Finder, and this article lays out the steps in clear outlines. Read on to find out about these steps, and to also find a top-draw answer to the question 'how can I edit file metadata in macOS 10.14?'

How to View Metadata in macOS 10.14 Mojave

There are a number of simple ways to look up file metadata in OS 10.14. The following is a rundown of two easy ways:

1. Using Finder:

When you highlight a file and then press 'Command'+ 'I', a Finder information pane opens to reveal the metadata of the file. This pane gives access to macOS mojave finder metadata of two categories: the first is the 'General' category which displays details such as the file’s format, size, date created and date modified, etc; and the other is the 'More Info' category which gives access to granular specifics of a file like dimension and color profile for image files, and composer, sampling rates, etc for music files.

2. Using The OS Terminal

Despite listing data in two separate categories, the Mac OS Mojave Finder metadata still comes short of a comprehensive collection of a file’s metadata. However, the Terminal’s 'mdls' command line gives access to a complete collection of a file’s metadata. To use the Terminal’s 'mdls' command line to reveal a files metadata, run the Terminal, and then key in 'mdls' followed by a single space. Next, drag and drop the select file from Finder to the open Terminal window, and then hit 'Enter'. After the Terminal successfully executes the command, a list pops up of all the metadata keys and values pertaining to the file. Each key begins with a 'kMDItem' prefix, for instance 'kMDItemPixelWidth' or 'kMDItemContentModificationDate'. The listing features a '=' sign that links each of the keys to their corresponding values.

The Terminal also allows you to access a specific metadata key of a file if you’re not looking for a rundown of the complete metadata. To do this, run the 'mdls' command using the command line scheme: mdls -name KEY FILEPATH

Where 'FILEPATH' represents the name of the select file, and 'KEY' represents the specific metadata key of the select file. There are a plethora of metadata keys that you can find using this command line. Some of the commonly used keys include:

Text

  • kMDItemAuthors
  • kMDItemAlternateNames
  • kMDItemContentCreationDate
  • kMDItemContentModificationDate
  • kMDItemContentType
  • kMDItemContentTypeTree
  • kMDItemCopyright
  • kMDItemDateAdded
  • kMDItemDisplayName
  • kMDItemFonts

Audio:

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  • kMDItemAudioBitRate
  • kMDItemAudioChannelCount
  • kMDItemAudioSampleRate

Movies:

  • kMDItemDurationSeconds
  • kMDItemVideoBitRate
  • kMDItemTotalBitRate
  • kMDItemStreamable

Images:

  • kMDItemHasAlphaChannel
  • kMDItemIsScreenCapture
  • kMDItemScreenCaptureType
  • kMDItemResolutionWidthDPI
  • kMDItemResolutionHeightDPI
  • kMDItemProfileName
  • kMDItemPixelWidth
  • kMDItemPixelHeight
  • kMDItemOrientation

How to Edit Metadata in macOS 10.14 Mojave

The file sorting and searching functions of Mac OS Mojave depend heavily on the metadata of files. Hence, when there are errors and mix ups in the metadata of a file, it becomes quite difficult to trace out the files in the drives. For instance, a music file with a wrong listing of the artist name and genre bears erroneous metadata. It’s commonplace to download or receive files that do not come with accurate metadata. Hence, it’s common for the question 'How can I edit file metadata in macOS 10.14' to cross the mind of a Mac user who’s yet to gain mastery over the metadata of files.

PDFelement provides Mac users with an expedient tool to edit metadata on PDF files. This gives users a wider span of control over the contents and information about PDF files. From structural to administrative and descriptive, PDFelement provides veritable tools for editing nearly every conceivable metadata of any PDF file.

PDFelement’s PDF file management solution offers multi-functional PDF editing tools for editing both the contents and the metadata of the contents of files. You can comment, add sticky notes, highlight, and do even more on the PDF file using PDFelement. You can also convert the PDF file to a wide array of file formats using PDFelement. In addition, PDFelement comes with an impressive array of security features for securing PDF files like the signature and password protection for files.

How to Edit PDF Metadata on macOS 10.14

After downloading and installing PDFelement on your device, you can then proceed to execute the following steps to edit the metadata of a PDF file:

1. Open the PDF file in PDFelement, and then select 'File' and then 'Properties'. This brings you to the 'Document properties' pane where you can get file metadata, including the author, subject, security status, etc.

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2. Once the file is open, and you can access the 'Properties' box, you can then proceed to effect changes in various aspects of the file, including the title, author, keywords, etc.

3. To remove an ill-fitting metadata key or value, simply select the undesirable key, and then hit 'Backspace' or 'Delete' key.

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