9. A computer storage medium encoded with a computer program, the program comprising instructions that when executed by data processing apparatus cause the data processing apparatus to perform operations comprising: receiving information specifying a first user interface at a client computer system, the first user interface enabling interaction with an existing application executed on an application server and being a standalone interface that is separate from the existing application; constructing one or more semantic operations by processing the information specifying the first user interface on the client computer system, each of the one or more semantic operations including sub-operations that are executable using user interface elements of the first user interface, the sub-operations comprising identifying a user interface element, selecting the user interface element, and inputting data using the user interface element; registering one or more voice commands to enable voice control of the first user interface and for initiating execution of the one or more semantic operations, each voice command corresponding to one of the semantic operations, the application executed on the application server remaining unmodified in view of the constructing one or more semantic operations and the registering one or more voice commands; displaying the first user interface at the client computer system upon registering the one or more voice commands; and performing one of the semantic operations in response to a first voice command, the first voice command not explicitly referencing the user interface element, wherein performing one of the semantic operations includes automatic execution of each of the sub-operations in response to the first voice command.
9. A computer storage medium encoded with a computer program, the program comprising instructions that when executed by data processing apparatus cause the data processing apparatus to perform operations comprising: receiving information specifying a first user interface at a client computer system, the first user interface enabling interaction with an existing application executed on an application server and being a standalone interface that is separate from the existing application; constructing one or more semantic operations by processing the information specifying the first user interface on the client computer system, each of the one or more semantic operations including sub-operations that are executable using user interface elements of the first user interface, the sub-operations comprising identifying a user interface element, selecting the user interface element, and inputting data using the user interface element; registering one or more voice commands to enable voice control of the first user interface and for initiating execution of the one or more semantic operations, each voice command corresponding to one of the semantic operations, the application executed on the application server remaining unmodified in view of the constructing one or more semantic operations and the registering one or more voice commands; displaying the first user interface at the client computer system upon registering the one or more voice commands; and performing one of the semantic operations in response to a first voice command, the first voice command not explicitly referencing the user interface element, wherein performing one of the semantic operations includes automatic execution of each of the sub-operations in response to the first voice command. 12. The computer storage medium of claim 9 , wherein the operations further comprise: identifying one or more graphical elements of the first user interface that may be controlled; registering one or more additional voice commands to enable control of the identified graphical elements of the first user interface, each additional voice command corresponding to at least one of the identified graphical elements; and controlling one of the identified graphical elements in response to a second voice command, the second voice command being one of the additional voice commands, the controlled graphical element corresponding to the second voice command.