Abstraction A simplification of something much more complicated that is going on under the covers. As it turns out, a lot of computer programming consists of building abstractions. What is a string library? It’s a way to pretend that computers can manipulate strings just as easily as they can manipulate numbers. What is a file system? It’s a way to pretend that a hard drive isn’t really a bunch of spinning magnetic platters that can store bits at certain locations, but rather a hierarchical system of folders-within-folders containing individual files that in turn consist of one or more strings of bytes.
DevOps DevOps is a cultural sensibility. It’s a unified, metrics based approach to making software efficiently and fearlessly using as much automation as possible.
Expression A fragment of code that produces a value is called an expression.
Higher Order Functions Functions that operate on other functions, either by taking them as arguments or by returning them..
Service Any processes, functionality, or data that must be discoverable and available over a network.
Transaction A transaction is a set of one or more statements that is executed as a unit, so either all of the statements are executed, or none of the statements is executed.
Why you may want to manage your own transactions is to maintain the integrity of your business processes. For example, if a customer places an order for some merchandise, the information you’d need to store for that order would include a list of items to purchase, billing and shipping information, and an authorized credit card charge. This information would likely be stored in several different tables. Without a manually managed transaction, it’s possible to enter part of the order, and then the system fails. The rest of the order information is then lost.
Transaction Level Dirty Read A transaction with an isolation level that allows for dirty reads implies that within that transaction you can see changes to data not yet committed by other transactions.