State-of-the-art automated stock trading

Usually, in a security exchange, exchanges maintain order book lists of all buy and sell orders with their quantity and prices, and they execute them when a match is found between somebody buying and selling. In addition, exchanges keep and provide statistics about state trading, often captured as OHCL (short for, open-high-close-low) and volume for both currencies of a trader pair.

By the way, bar charts are used, showing open, high, low, and closing prices. Unlike line charts, OHLC charts enable technical analysts to evaluate intra-day volatility and see where prices opened and closed. Take a look at this diagram:

OHLC pricing model showing the open, high, low, and close prices of a certain time period (source: http://en.tradimo.com/tradipedia/ohlc-chart/)

This data is being presented as aggregated in some periods, from seconds to days...