JNTU B.Tech III PRINCIPLES OF PROGRAMMING LANGUAGES Previous Question Paper (August/September - 2024 - R13)

Attributed grammars are an extension of context-free grammars where each grammar symbol is associated with a set of attributes. These attributes can hold semantic information about the program construct represented by the symbol. Attributes can be of two types: synthesized (computed from children) and inherited (passed down from parent).

Example:

Consider a simple grammar for arithmetic expressions:

E -> E + T | T

T -> T * F | F

F -> ( E ) | id

With attributed grammars, we can add attributes to track the value of the expression. For instance, for the non-terminal 'E', we can have a synthesized attribute 'val' which stores the computed value of the expression.

E.val = E1.val + T.val

E.val = T.val

T.val = T1.val * F.val

T.val = F.val

F.val = E.val

F.val = id.value

A virtual machine (VM) is a software-based emulation of a physical computer. It runs on top of a host operating system and provides an environment where applications can execute as if they were running on their own dedicated hardware. VMs abstract the underlying hardware, allowing multiple operating systems and applications to run concurrently on a single physical machine.

Key aspects include:

• Abstraction: VMs hide the complexities of the physical hardware from the guest operating system and applications.
• Isolation: Each VM is isolated from the host system and other VMs, enhancing security and stability. If one VM crashes, it doesn't affect others.
• Portability: VMs can be easily moved or copied between different physical machines, facilitating development, testing, and deployment.
• Resource Management: The hypervisor (VM monitor) manages and allocates physical resources (CPU, memory, storage, network) to the VMs.

Examples include VMware, VirtualBox, and Hyper-V.