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+Use-case with eTags
+###################
+We explain the use-case of tagging a device with an :ref:`tags:eTags`,
+going through the manufacturing of the tags, their distribution and
+the final linkage between tag and computer.
+
+For this use-case we suppose we want 100 eTags.
+
+Actors
+******
+
+- Tag provider: organization that orders and manages the eTags; it is
+  certified by eReuse.org thus having permission to order the tags.
+- NFC Tag manufacturer.
+- Photochromic tag manufacturer.
+- User: organization that uses the tags.
+
+
+Requirements
+************
+
+- At least one eReuse.org Devicehub. One Devicehub can contain several
+  organizations and inventories, or organizations can have their own
+  copy of Devicehub. Devicehub work distributely over the Internet.
+- One `eReuse.org Tag <https://github.com/ereuse/tag>`_ running in a
+  server over the Internet by the *tag provider*.
+
+Use case
+********
+
+1. The *tag provider* enters into the server containing the
+   *eReuse.org Tag* software and executes the command
+   ``etag create-tags 100 --csv file.csv``, which creates 100
+   tags in the database and saves their URLs into a spreadsheet CSV file
+   called *file.csv*.
+2. The *tag provider* sends the CSV file to the *NFC tag manufacturer*
+   and orders the 100 tags.
+3. The *NFC tag manufacturer* creates those tags (NFC plus QR code)
+   and updates the CSV file with the NFC ID of each tag, so each row
+   of the CSV file contains the URL sent by the *tag provider* and
+   the ID of the NFC tag created by the *NFC tag manufacturer*.
+4. The *Tag provider* updates *eReuse.org Tag* with the ID of the
+   NFC by executing ``etag update-tags file.csv`` where *file.csv* is the
+   file sent by the *NFC tag manufacturer*.
+5. The *Tag provider* orders 100 photochromic tags to the *Photochromic
+   tag manufacturer*. Note that these tags don't require any special
+   treatment.
+6. The *Photochromic tag manufacturer* sends back 100 tags.
+7. The *Tag provider* distributes the eTags (NFC and photochromic) to
+   several organizations, *users*, both physically by sending them and
+   virtually by executing ``etag set-tags http://some-devicehub.com
+   0 100``; this marks the tags in *eReuse.org Tag*
+   as *sent to some-devicehub.com* and creates the tags in that
+   Devicehub.
+8. The *user* receives the tags, sticks them in their devices, and scans
+   the NFC or QR codes:
+
+   1. By using the `eReuse.org Android App <https://github.com/eReuse/eReuseAndroidApp>`_
+      the user can scan the QR code or the NFC of the eTag.
+   2. If the *user* is processing devices with the `eReuse.org
+      Workbench <https://github.com/ereuse/workbench>`_, Workbench
+      automatically attaches hardware information like serial numbers,
+      otherwise the *user* can add that information through the app.
+   3. These softwares communicate with the Devicehub of the user and
+      command the Devicehub to link the device with the tag.
+   4. The Devicehub of the user links the tag.
+   5. The Devicehub creates or updates a virtual entity in Everythng
+      containing the device and the tag.
+   6. If Devicehub or Everythng detect that the tag was linked they won't
+      allow this operation. Devicehub can only detect if the app is linked
+      by looking at its internal database. Everythng, as it contains all
+      device and tag information, validates that the tag is not linked
+      elsewhere.