DOCS-648 migrate tutorial wiki to getting started page

Author: Bob Grabar

draft/core/schema-free.txt

@@ -0,0 +1,27 @@
+============================
+Dynamic Schema (Schema Free)
+============================
+
+.. default-domain:: mongodb
+
+MongoDB has :term:`databases <database>`, :term:`collections
+<collection>`, and :term:`indexes <index>` much like a traditional
+RDBMS. In some cases (databases and collections), these can be
+implicitly created. Once created, they exist in a system catalog
+(for example, ``db.systems.collections``, ``db.system.indexes``).
+
+Collections contain :term:`BSON` :term:`documents <document>`. Within
+these documents are fields. In MongoDB there is no predefinition of
+fields (what would be columns in an RDBMS). There is no schema for
+fields within documents. The fields and their value datatypes can vary.
+Thus there is no notion of an "alter table" operation that adds a
+"column".
+
+In practice, it is highly common for a collection to have a homogenous
+structure across documents. Hoowever this is not a requirement. This
+flexibility means that schema migration and augmentation are very easy
+in practice. Rarely will you need to write scripts that perform "alter
+table" type operations. In addition to making schema migration flexible,
+this facility makes iterative software development atop the database
+easier.
+