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Kevin started off by listing out the four types of Nosql databases, which are:

While there are a number of NoSql databases out in the market currently, MongoDB is the leading Open-Source, NoSql database available. MongoDb has a flexible schema, which means that the collections are not bound in a fixed document. The collections in MongoDB are stored in documents called BSON or Binary JSON. The structure of a BSON document is same as a JSON document, which means that every collection in Mongo is enclosed in curly brackets just like a JSON document. When saying Mongo has a flexible schema it means that when a collection has, for example 4 fields, data with number of fields other than 4 can be added to the same collection. The collections are not schema bounds like relational databases. Being schema-less also means that, common fields in a document's collection can hold different types of data. For example, a field which is used for Name can hold characters, decimal values, integers etc. This does not work in relational databases because, in relational databases when a field is defined as a particular data type it can only hold values of that data type. This illustrates the flexibility of MongoDB.