Update README.md

Author: npbhoang

README.md

@@ -2,3 +2,42 @@
 
 A representation of OCL expression in Java.
 
+This table represents a detailed overview of supported Object Constraint Language (OCL) operators in our implementation `OCL2PSQL`. It consists of several categories, in which contains 2 columns: the operator (on the left) and the syntax example (on the right).
+
+##### Class operations
+|||
+|--------------------------|---|
+|`allInstances`  |  *class*.`allInstances()` |
+|`attributes`  |  *var*.`att` |
+|`association ends`  |  *var*.`assoc` |
+
+##### Constants operations
+|||
+|--------------------------|---|
+|`Boolean Literal`  |  `{TRUE, FALSE}`|
+|`Integer Literal`  |  `{..., -2, 1, 0, 1, 2, ...}`|
+|`String Literal`  |  `'string'`|
+
+##### Boolean operations
+|||
+|--------------------------|---|
+|`not`  |  `NOT` *bool-expr* |
+|`and`, `or`| *bool-expr* `logic-operator` *bool-expr'*|
+| =, <>, >, <, &#8805;, &#8804;  |  *bool-expr* `compare-operator` *bool-expr'*|
+
+##### Iterative operations
+|||
+|--------------------------|---|
+|`collect`  |  *source-expr* -> `collect`(*var* &#124; *body-expr*) |
+|`forAll`  |  *source-expr* -> `forAll`(*var* &#124; *bool-expr*) |
+|`exists`  |  *source-expr* -> `exists`(*var* &#124; *bool-expr*) |
+|`select`  |  *source-expr* -> `select`(*var* &#124; *bool-expr*) |
+|`reject`  |  *source-expr* -> `reject`(*var* &#124; *bool-expr*) |
+|`size`  |  *source-expr* -> `size()`|
+|`isEmpty`  |  *source-expr* -> `isEmpty()`|
+|`notEmpty`  |  *source-expr* -> `notEmpty()`|
+|`isUnique`  |  *source-expr* -> `isUnique()`|
+|`flatten`[<sup>1</sup>]  |  *source-expr* -> `flatten()`|
+
+###### [<sup>1</sup>] For the time being, this can operate *ONLY* after the `collect` operation
+[<sup>1</sup>]:#-For