What Does Concordance Mean?

I was having dinner with a client on Monday night and the following question came up:  How did we come up with name "Concordance" for our reference data/company identifier mapping product?  The client remarked that he knew what we meant by Concordance but that in some cases it was hard to effectively describe it to colleagues. 
I got back to the office and, since I had forgotten the origin of Alacra Concordance, I asked around. It turns out that we had heard the term from a customer and after some research we adopted it as our own.  There are several related definitions of concordance from Dictionary.com:

1.	agreement; concord; harmony: the concordance of the membership.

2.	an alphabetical index of the principal words of a book, as of the Bible, with a reference to the passage in which each occurs.

3.	an alphabetical index of subjects or topics.

4.	(in genetic studies) the degree of similarity in a pair of twins with respect to the presence or absence of a particular disease or trait.

Alacra Concordance is the mapping of all the various company identifiers that are used by all of our content partners.  The mapping includes ticker, ISIN, CUSIP, Sedol, Duns number, issuer IDs from the ratings agencies, Markit Red Codes, KMV PIDs and many more.  Without Concordance we couldn't provide all the possible results from a federated search across all our databases.  All the identifers need to agree, or be in harmony with the Alacra Company ID.  While this may appear simple, it's actually quite challenging in that we cover several hundred thousand companies and the concordance file needs to reflect corporate actions accurately and in a timely fashion.  If you're familiar with security master file or reference data, you'll understand the difficulty in mapping over 35 different identifiers. It was the concept of a comprehensive index that was in agreement that led us to use the term concordance.  [This is the first in a series on Alacra Concordance.]