NoSQL data architecture patterns - Making Sense of NoSQL - page 68

Standards watch: complex APIs can still be portable if they're standardized
and have portability tests
It's important to note that complex interfaces can still permit high portability. For
example, XQuery, a query language used in XML systems, has hundreds of functions,
which can be considered a complex application-database interface. But these func-
tions have been standardized by the World Wide Web (W3C) and are still considered
to be a low-cost and highly portable application-database interface layer. The W3C
provides a comprehensive XQuery test suite to verify if the XQuery interfaces are con-
sistent between implementations. Any XQuery implementation that has over a 99%
pass rate allows applications to be ported without significant change.

4.1.3 Using a key-value store

Let's take a look at how an application developer might use a key-value store within an
application. The best way to think about using a key-value store is to visualize a single
table with two columns. The first column is called the key and the second column is
called the value . There are three operations performed on a key-value store: put, get,
and delete. These three operations form the basis of how programmers interface with
the key-value store. We call this set of programmer interfaces the application program
interface or API . The key-value interface is summarized in figure 4.5.
Instead of using a query language, application developers access and manipulate a
key-value store with the put , get , and delete functions, as shown here:
1 put($key as xs:string, $value as item()) adds a new key-value pair to the
table and will update a value if this key is already present.
2 get($key as xs:string) as item() returns the value for any given key, or it
may return an error message if there's no key in the key-value store.
3 delete($key as xs:string) removes a key and its value from the table, or it
many return an error message if there's no key in the key-value store.

Inputs Key Value Outputs

1 PUT 123 value123 123 value123

2 GET 456 456 value456 value456

3 DELETE 789 789

Figure 4.5 The key-value store API has three simple commands: put , get , and
delete . This diagram shows how the put command inserts the input key "123" and
value "value123" into a new key-value pair; the get command presents the key
"456" and retrieves the value "value456" ; and the delete command presents the
key "789" and removes the key-value pair.