ABSTRACT
In previous chapters, we have encountered some useful tools for specific computing tasks. For example, in Chapter 7 we learned about SQL for extracting data from a relational database.
Given a data set that has been stored in a relational database, we could now write a piece of SQL code to extract data from that data set. But what if we want to extract data from the database at a specific time of day? What if we want to repeat that task every day for a year? SQL has no concept of when to execute a task.
