A data dictionary (A) is the authoritative source for understanding: * Data types and numeric formats * Valid ranges and interpretations * Field definitions and business meaning * Normalization and scaling expectations Before balancing or preprocessing data, developers must verify that they understand each feature correctly. The AAIA framework emphasizes that misinterpretation of numeric variables often leads to: * Incorrect normalization * Faulty scaling * Skewed class balancing * Inaccurate model training Statistical summaries (C) help identify distributions but cannot validate semantic meaning. Confusion matrices (D) are used after training. Libraries (B) are tools, not sources of interpretation. References: AAIA Domain 2: Data Management - Data Dictionaries, Metadata, Data Understanding