I have been looking in to NoSQL databases for few months and would like to share my experience with it. This is a post might help you if you indent to start learning about the NoSQL Databases . I would try to link the resources which I found useful here.
Step 1: What is NoSQL?
NoSQL DEFINITION : Next Generation Databases mostly addressing some of the points: being non-relational, distributed, open-source and horizontally scalable. The original intention has been modern web-scale databases. The movement began early 2009 and is growing rapidly. Often more characteristics apply such as: schema-free, easy replication support, simple API, eventually consistent / BASE (not ACID), a huge amount of data and more. So the misleading term "nosql" (the community now translates it mostly with "not only sql").
As seen on NoSQL-Database.org.
Martin Flower'sNoSQL page is a good starting point. His below talk on Goto Conference explains the need and structure of NoSQL data stores. Martin and Pramod has written a book titled "NoSQL Distilled: A Brief Guide to the Emerging World of Polyglot Persistence" and is a good read. It summarizes his talks and other blog post into a book. Martin has been an influential speaker on this topic and has written number of articles on this. I have read and seen many introductions but his work helped me to get things in to my head.
If you likes to view the slides, then the below presentation by Tobias Lindaaker on slideshare might inspire you. He gives similar ideas.
MongoDB has an online course MongoDB for Java Developers which is really useful if you are interested in trying out things.
Step 2: How and for what are NoSQL used in Real world?
Once you have some idea, try to find the usage patterns. The above presentations will give lot of information on how these systems are used. You could go through the below links, which explains how specific business problems are solved using NoSQL. This is important because we could easily relate the case studies and get more insights into the capabilities of these systems.
1. MongoDB Customers page.
2. Powerd By Haddop
3. Neo4J Customers Page
Step 3 : Find Usage Patterns that you could work on!
Once you have reached this point, you should try and implement the concepts. Look back at the application that you are working on and see if there is a need for an alternative data store. Do you store Product recommendations? Do you have issues with heterogeneous data? Can your application compromise ACID model for scalability? Do you store XML files or Images on you relational DB? These are some of the questions that you could ask. This way you could determine if there is a serious need of a investigation for a alternative persistence mechanisms. This is in no way means removing the RDBMS completely but moving to a polygot structure of data stores.
If there is no opportunity to try out these concepts in your work, you could create your own test projects and implement them. This way you would encounter problems and will learn from them.