# Monitoring and Observability (Data Engineering) > Structured logging, metrics, alerting, SLA/SLO/SLI, data quality checks, Great Expectations, Soda - 20 interview questions - Senior - [Interview Questions: Data Engineering](https://sharpskill.dev/en/technologies/data-engineering/interview-questions.md) ## 1. What is structured logging in the context of a data pipeline? **Answer** Structured logging means emitting logs in a parsable format (JSON, key-value) rather than free text. This allows easy filtering, searching and aggregating logs in tools like Cloud Logging, Elasticsearch or Datadog. In a data pipeline, this greatly facilitates debugging by enabling filtering by DAG, task_id, run_id or any business context. ## 2. What is the difference between an SLI (Service Level Indicator) and an SLO (Service Level Objective)? **Answer** An SLI is a measurable metric that quantifies an aspect of service quality (e.g., job success rate, pipeline latency). An SLO is a target defined on that metric (e.g., 99.5% of jobs must succeed). The SLA is the contractual commitment to customers based on internal SLOs. This hierarchy enables objective reliability monitoring and triggering alerts before violating SLAs. ## 3. What is an Expectation in Great Expectations? **Answer** An Expectation is a declarative assertion about data, like expect_column_values_to_not_be_null or expect_column_values_to_be_between. Great Expectations automatically generates documentation and actionable validation results. These Expectations are grouped into Suites that define the complete quality contract for a dataset. ## 17 more questions available - What is the main role of Soda in a data pipeline? - What is a runbook in the context of data incident management? 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