How can I find other CDs or MP3 downloads by the same artist?

Unfortunately, there is no definite way to find all the CDs or MP3s associated with the same artist as a given CD or MP3.

The best you can do is to find the ASIN of the Artist ASIN associated with the CD or MP3 download. Once you know the Artist ASIN you can link to the artist's page at Amazon.com or update a local database that you can use to relate CDs and MP3s by artist.

To find the Artist ASIN for a CD or MP3 download, use the following techique.

Use the RelationshipType parameter with the RelatedItems response group to find the parent album associated with a CD or MP3 album download.

For example, consider the album At San Quentin by Johnny Cash. The ASIN of the CD version of the album is B00004U2GH. To find the ASIN for the parent of the album, do an ItemLookup on the CD's ASIN (B00004U2GH) with RelationshipType=AuthorityTitle:

>>> View ItemLookup for B00004U2GH

In the RelatedItems element, you find the ASIN of the album's parent - B000B4TCPE.

Do basically the same ItemLookup on the parent ASIN (B000B4TCPE):

>>> View ItemLookup for B000B4TCPE

In the RelatedItems element you'll see the ASINs of various versions of the album. The web service lists a maximum of 10 related items per query. If the query results in more than 10 releated items, add the RelatedItemPage parameter to your query and set it to "2" to return the second page of ten related items, "3" to return the third page, etc.

Do an ItemLookup on each of the ASINs in RelatedItems using RelationshipType=DigitalMusicPrimaryArtist. These can be combined into one query as follows.

>>> View ItemLookup for B00004U2GH,B00004U2GI,B00005QVHD,B0013D8EQK

In the RelatedItems element of the response, you will find the ASIN of the Artist (B000QJO1ZA).

You can link to the artist's page at Amazon.com using the Artist ASIN:

http://www.amazon.com/dp/B000QJO1ZA/?tag=YourAssociatesId

If your site uses a database, you can store the artist's name and ASIN in a table. For each MP3 download and CD, you can use the above technique to find the associated artist's ASIN. Store the album or track's ASIN and the artist's ASIN in a table that you can use to relate CDs and MP3s to a specific artist.