Kleppmann, Martin

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Part I. Foundations of Data Systems

✅ Ch 01. Reliable, Scalable and Maintainable Applications:

• ✅ Thinking About Data Systems
• ✅ Reliability: hardware faults; software errors; human errors; importance of reliability.
• ✅ Scalability: describing load; describing performance; approaches for coping with load.
• ✅ Maintainability: operability - making life easy for operations; simplicity - managing complexity; evolvability - making change easy.

Ch 02. Data Models and Query Languages:

Query Languages for Data

If you have a list of animal species and you want to return only the sharks in the list, a relational algebra expression would be \( \text{sharks} = \sigma_{\text{family = “Sharks”}}(\text{animals}) \). SQL queries follow the structure of relational algebra closely:

SELECT * FROM animals WHERE family = 'Sharks';

… while an imperative query would be:

function getSharks() {
  let sharks = [];
  for (let i = 0; i < animals.length; i++) {
    if (animals[i].family === "Sharks") {
      sharks.push(animals[i]);
    }
  }
  return sharks;
}