So a federation is how things collaborate / work together for a greater good and how a number of things bubble up into a larger collective. So how does this apply to the idea of federated databases. Federated databases provide technologies to make a collection of databases look like a single database. This is a simplified description that will do for the scope of this post. A good way to describe database federation is to compare it to a centralized database. 1. A group of states with a central government but independence in internal affairs.
2. An organization or group within which smaller divisions have some degree of internal autonomy.
|Centralized vs Federated databases
Example: a federation of digital badges
Currently there are a number of emerging digital badge systems. Each of these different systems is designed to serve their particular badge issuer needs. Each has both similar and different attributes for what is a digital badge. A basic comparison of their similarities and differences would assist in describing a federation of digital badges. The following five sites issue digital badges, and each of them store user data regarding their earned badges in a database hosted on their respective servers;
- khan academy - https://github.com/Khan/khan-api
- codeacademy - http://www.codecademy.com
- foursquare - https://developer.foursquare.com/
- stackoverflow - https://api.stackexchange.com/
- mozilla open badges - http://beta.openbadges.org
- badge criteria - the implementation of badge criteria can vary. It varies from a simple url location (mozilla), a collection of other badges or accomplishments (khan), and a dynamic criteria based on live contribution data (stackoverflow).
- badge evidence - can also vary in its implementation, some of the evidence will follow the format required / specified by the criteria. While other evidence formats include a variety of different media and online contributions.
- badge name - the title of the badge
- badge description - the description of the badge
- issuer url - the internet url of the badge issuer
- badge image - the url of the image used
- earner identifier - the unique identifier of the badge earner
- earner email - the earner email address
To create a federated database of these different badge systems all the data would be merged. The similar data fields could be easily merged for the format is the same and would require no transformation. The different data fields could also be merged with some transformations, though it is likely some detail would be lost having the differences conform to the similar structure. If all goes well from a merge and data transformation perspective you would end up with a single view into all the different badge systems.
Note 2: Federated systems can have different amounts of merge and transform. In some situation the data is copied and moved into a new database that contains the federated data. In other situations technology sits on top of all the different databases and the merge and transform occurs in real-time and no data is moved or copied.
Note 3: This is a simplified discussion of federated databases. There are many design and technical details that have been simplified for this discussion. Feel free to email me if you would like to engage in a deeper discussion about database federation.