Data Dependency:  It refers to the state in which two or more instructions split same data. The instructions in a program can be given based on the relationship of data dependency; this means how two segments or instructions are data dependent on each other. The following types of data dependencies are:

i)  Flow Dependence : If instruction I2 follows I1 and output of I1 turn into  input of

I2, then I2 is called to be flow dependent on I1.

ii)  Antidependence : When instruction I2 follows I1 such that output of I2 overlie

with the input of I1 on the similar data.

iii) Output dependence : When output of the two instructions I1 and I2 overlie on

the similar data, the instructions are supposed to be output dependent.

iv) I/O dependence : When read and write operations by two instructions are raised on the similar file, it is a position of I/O dependence.

Let Consider the following program instructions:

                                                                              I₁: a = b

                                                                          I₂: c = a + d

                                                                              I₃: a = c

In this program section instructions I₁ and I₂ are Flow dependent as variable  is used by I₂ as input and generated by I₁ as output.Here, Instructions I₂ and I₃ are Antidependent as variable is produced by I₃ but used by I₂ and in order I₂ comes first. I₃ is flow dependent on I₂ because of variable c. Instructions I₁ and I₃ are Output dependent because variable a is produced by both instructions.