About Apache Cassandra

From Wikipedia - “Apache Cassandra is a free and open-source distributed NoSQL database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure”.

Features of Apache Cassandra

1. Decentralized. No master node. Multiple nodes in a cluster. Data is distributed across nodes
2. Replication supported across multiple data centers.
3. Scalable - Throughput increase linearly with new machines
4. Fault-tolerant - Failed nodes can be replaced with no downtimes
5. Flexible consistency

Source code:

Version: cassandra-3.9

Arduino UNO R2 expained: This arduino has two mcu - Atmega8u2 and Atmega328. Atmega8u2 has the DFU bootloader and the usb-serial firmware loaded to it by default. The usb-serial firmware is what reads the usb in buffer and converts it to serial data for the main chip - Atmega328 to process.

DFU bootloader: The DFU bootloader allows you to update the firmware in Atmega8u2 without an ISP(In system programmer).

Bootloader: This bootloader in Atmega328 is the one that loads the main program stored in flash. When the arduino is plugged in, this bootloader runs and then the main program starts running.

More to follow..

Recursive descent parsing algorithm.

Backus normal form:

It is a system that describes grammar of natural language. The power of BNF is in its recursive nature.

BNF for a while loop:

<while-loop> ::= "while" "(" <condition> ")" <statement>

Recursive descent parser:

This parser is most suited for written by hand.

An example parser for the BNF below:

<expression>  ::=  <Integer>  |
               "(" <expression> <operator> <expression> ")"
               
<operator>  ::=  "+" | "-" | "*" | "/"

IO class:

methods:

peek, skipBlanks, getChar, getInt()

Parser Class:

methods:

getOperator, expressionVal

Writing a parser with operator precedence:

This depends on how the BNF rules are written:

((3*2) + 2 / 4 )

The operation happens with /,* and then it adds the two results.

((3*2) + 2), 4 are two factors.

3*2 is a term which is a combination of two factors. And the final expression is a (+,-) combination of terms.

In BNF:

<expression> := [-] <term> | [+|- <term>].. 
<term> := <factor> | [*|/ <factor>]..
<factor> := <number> | "(" <expression> ")"

[].. is repeated zero to many times. so that constitutes a while loop.

Also added a parser program with expression tree.

Source: parser