Answers.Body: <p>The dc:identifier is commonly an ISBN, though any sort of <a href="http://en.wikipedia.org/wiki/Uniform_resource_name">URN</a> will do. Further information about using  in epub can be found on the <a href="http://www.idpf.org/epub/30/spec/epub30-publications.html#sec-opf-dcidentifier">IDPF's site</a>, but as a quick example, you could use something like:</p>
  
  <pre><code>&lt;dc:identifier id="isbn"&gt;urn:isbn:0451450523&lt;/dc:identifier&gt;
  </code></pre>
  
  <p>As long as the identifier is unique, it should be fine. At the above link, the IDPF says:</p>
  
  <blockquote>
    <p>Every metadata section must include at least one identifier element
    containing an unambiguous identifier for the Publication. Multiple
    identifier elements are permitted, but only one can be marked as the
    Unique Identifier via the package element unique-identifier attribute.</p>
  </blockquote>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-03-04T18:59:06.590Z
Answers.Text: Because of the cost involved, only those EPUB 3.0 publications that are commercially published can be expected to use an ISBN as primary ID. So although these can, and will exist, they are not common, and will be a tiny minority of all EPUB 3.0 publications.
  I have a 5000+ EPUB 3.0 files and none of them have an ISBN and all have a UUID as primary ID.
Answers.UserDisplayName: Anthon
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-06-02T18:31:27.757Z
Answers.Text: @Anthon, bear in mind that cost depends to a certain extent on where you are. For example, ISBNs are free in Canada, apparently.
Answers.UserDisplayName: Tom
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-03-04T18:12:51.240Z
Answers.LastActivityDate: 2014-03-04T18:12:51.240Z
Answers.UserDisplayName: Tom
Answers.Body: <p>Yes it should be unique, and no, it is not hased to an IP or MAC address.</p>
  
  <p>The example in the <a href="http://www.idpf.org/epub/30/spec/epub30-publications.html#sec-opf-metadata-identifiers-pid" rel="nofollow">EPUB 3.0 specification</a> uses a <a href="https://en.wikipedia.org/wiki/Universally_unique_identifier" rel="nofollow">UUID</a>.
  The particular UUID used in the example is:</p>
  
  <pre><code>A1B0D67E-2E81-4DF5-9E67-A64CBE366809
  </code></pre>
  
  <p>And the <code>4</code> in the position directly after the second <code>-</code> indicates that it is a <a href="https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_.28random.29" rel="nofollow">random UUID</a>. The UUID linked to a MAC address is version 1.</p>
  
  <p>There is however, no necessity that this is a UUID. The only premise is that</p>
  
  <blockquote>
    <p>a primary identifier that is unique to one and only one particular EPUB Publication</p>
  </blockquote>
  
  <p>E.g. the <a href="https://code.google.com/p/epub-samples/downloads/list" rel="nofollow">epub 3 examples</a> mostly use a URN, and AFAIK none of those use an ISBN. </p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-03-04T18:39:30.583Z
Answers.LastActivityDate: 2014-03-04T18:55:28.027Z
Answers.LastEditDate: 2014-03-04T18:55:28.027Z
Answers.UserDisplayName: Anthon
Body: <p>My question is on the <code>&lt;dc:identifier&gt;</code>. Is the <code>&lt;dc:indentifier&gt;</code> unique and hashed to an IP address or MAC address? </p>
  
Tags: <epub><privacy><metadata><opf>
Title: EPUB 3.0 <dc:identifier>
UserDisplayName: Abu Landowner
ThreadText: # EPUB 3.0 <dc:identifier>
  
  (Asked by: username_0 on 2014-03-04)
  
  My question is on the . Is the  unique and hashed to an IP address or MAC address?
  
  **Tags:** epub, privacy, metadata, opf
  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_1 on 2014-03-04. Score: 7
  
  The dc:identifier is commonly an ISBN, though any sort of URN will do. Further information about using  in epub can be found on the IDPF's site, but as a quick example, you could use something like:
  urn:isbn:0451450523
  
  As long as the identifier is unique, it should be fine. At the above link, the IDPF says:
  
  Every metadata section must include at least one identifier element
    containing an unambiguous identifier for the Publication. Multiple
    identifier elements are permitted, but only one can be marked as the
    Unique Identifier via the package element unique-identifier attribute.
  
  > **Comments:**
  > **username_2**: Because of the cost involved, only those EPUB 3.0 publications that are commercially published can be expected to use an ISBN as primary ID. So although these can, and will exist, they are not common, and will be a tiny minority of all EPUB 3.0 publications. I have a 5000+ EPUB 3.0 files and none of them have an ISBN and all have a UUID as primary ID.  
  > **username_1**: @username_2, bear in mind that cost depends to a certain extent on where you are. For example, ISBNs are free in Canada, apparently.  
  
  ---
  
  ### Answer by username_2 on 2014-03-04. Score: 4
  
  Yes it should be unique, and no, it is not hased to an IP or MAC address.
  The example in the EPUB 3.0 specification uses a UUID.
  The particular UUID used in the example is:
  A1B0D67E-2E81-4DF5-9E67-A64CBE366809
  
  And the 4 in the position directly after the second - indicates that it is a random UUID. The UUID linked to a MAC address is version 1.
  There is however, no necessity that this is a UUID. The only premise is that
  
  a primary identifier that is unique to one and only one particular EPUB Publication
  
  E.g. the epub 3 examples mostly use a URN, and AFAIK none of those use an ISBN.
  
  
  ---
  
  