Generate a dataset from a schema

Generate a dataset from a schema you design. This is the primary Misata tool.

DIVISION OF LABOUR You (the agent) design what the data should look like — the tables, columns, business rules, and declared targets. Misata handles the hard guarantees: every FK resolves, every rollup reconciles to the cent, every declared outcome curve is hit exactly, every seed produces byte-identical output. The response includes a per-relationship integrity proof.

SCHEMA FORMAT {table_name: {column_name: spec, ...}, ...}

TABLE-LEVEL KEYS (inside a table dict) "rows": 5000 Per-table row count; overrides the global rows arg. Always set this — one global count rarely fits all tables. "constraints" List of row-level business rules (see CONSTRAINTS below). "correlations" List of pairwise Pearson targets (see CORRELATIONS below). "state_machine" Markov terminal-state assignment (see STATE MACHINE below).

COLUMN TYPES integer, float, decimal Numeric. string Short categorical or free text. text Long free text (descriptions, notes). email, phone, url, uuid Semantic strings; always valid format. date, datetime Temporal; realistic granularity applied automatically. boolean True/False with declared probability.

COLUMN SPEC KEYS (inside a column dict) primary_key: true Auto-incremented PK; column excluded from CSV output. foreign_key: {table, column} Child FK; referential integrity guaranteed + verified. min / max Numeric or date bounds. decimals: 2 Decimal places for float output. unique: true All values in the column are distinct. nullable: true Allow nulls (default true). enum: [...] Categorical choices. Add probabilities: [...] for weights; omit for realistic Zipf-shaped rank frequencies. probabilities: [...] Weights for enum choices; must sum to 1.0.

DISTRIBUTIONS (float / integer columns) distribution: normal Also: lognormal, uniform, exponential, beta, poisson, power_law, gamma. mean / std Normal params. Can be a scalar OR a per-row parent-entity lookup: mean: {formula: "@patients.hba1c_baseline"} The FK is resolved per-row so each child row's distribution is anchored to its parent's value. Use this for longitudinal data where within-entity variation should be modelled separately from between-entity variation. mu / sigma Lognormal params (mu and sigma are of log(x)). min / max Hard clamps applied after sampling. Use lognormal for money, file sizes, session durations — anything right-skewed and strictly positive. Use normal for measurements.

DERIVED COLUMNS formula: "quantity * unit_price" Row-level arithmetic; pandas eval syntax. formula: "hours * @employees.rate" Cross-table via FK: @parent_table.column. rollup: {from_table, fk, agg, column} Parent column that EXACTLY reconciles with child rows under JOIN. agg: sum/count/mean/ max/min. Add where: {col: val} to filter. RULE: use rollup (not formula) for any parent column that summarises child rows. Rollups are closed-form exact; formulas cannot cross the FK boundary correctly.

CODE-STYLE STRINGS pattern: "SKU-\d{5}" Single pattern expanded per row. pattern: ["A/\d{5}", "\d{6}"] List: one shape drawn per row. pattern_weights: [0.7, 0.3] Weights for pattern list (optional). Supported tokens: \d (digit), [A-Z] (uppercase letter), [a-z] (lowercase), literal chars, {n} repeat count. Example: "[A-Z]{2}-\d{4}" → "AB-3721".

TEXT SEMANTICS text_type: person_name Always beats column-name inference. Options: person_name, email, company, city, country, postal_code, phone, url, description, username, product_name, review_text, address, job_title. Dates: appointment times snap to 15-min business-hours grids; signups follow waking-hour rhythms; machine events keep sub-second precision. Names, genders, and emails are generated jointly and always agree.

STRATIFIED DISTRIBUTIONS (profiles) Use when different subgroups need different distributions for the same column. profiles: [ {when: "arm == 'placebo'", distribution: normal, mean: -0.35, std: 0.50}, {when: "arm == 'high_dose'", distribution: normal, mean: -1.25, std: 0.55}, ] Rows that match no profile get the column's top-level distribution. The when expression is a pandas eval string; reference any already-generated column in the same table. Always list profiles after the columns they reference.

INFORMATIVE MISSINGNESS (MAR) null_when: "dropout == False" Null this column when expression is true. missing_if: Missing-At-Random tied to a predictor column. predictor: hba1c_baseline relationship: higher_increases_probability # or lower_increases_probability base_rate: 0.05 # null probability at predictor median max_rate: 0.40 # null probability at predictor extreme Use null_when for status-conditional nulls (dropout_visit is null when not dropped out). Use missing_if when missingness is correlated with an observed variable.

EXACT INCIDENCE CONTROL exact_incidence: Hit the declared count exactly (not approximately). mode: exact rate: 0.22 # exactly floor(n * 0.22) rows become True group_by: arm # optional: apply per group rates: {placebo: 0.15, high_dose: 0.55} # per-group exact rates Use exact_incidence instead of probability on boolean columns when the user states a precise rate that must hold in the data, not just on average.

WITHIN-ENTITY TIME SERIES (longitudinal autocorrelation) time_series: Re-writes a column to have AR1 autocorrelation entity_id: patient_id within each entity group. order_by: visit_number model: AR1 # AR1 | linear_trend | random_walk | mean_reversion phi: 0.72 # autocorrelation coefficient (AR1 only) noise_std: 0.30 anchor_column: hba1c_baseline # starting value (column in the same table) trend: slope_mean: -0.08 # mean drift per step slope_std: 0.02 # per-entity slope variability Required for any longitudinal dataset (clinical visits, IoT sensors, user sessions). Without it every row is independent and the data fails any time-series test.

CONSTRAINTS (table-level constraints list) {"type": "inequality", "column_a": "visit_date", "operator": ">=", "column_b": "enroll_date", "action": "cap"} Enforces column_a OP column_b. action: "cap" (snap column_a to column_b) or "drop" (remove violating rows). Works on dates and numerics. {"type": "col_range", "low_column": "min_price", "column": "price", "high_column": "max_price", "action": "cap"} Keeps low_column <= column <= high_column. {"type": "max_per_group", "group_by": "user_id", "max_count": 3} Limits rows per group value. {"type": "unique_combination", "columns": ["user_id", "product_id"]} No duplicate (col_a, col_b) pairs. Use constraints for any business rule that must hold on every row: visit_date >= enrollment_date, price > cost, resolution_day > onset_day.

CORRELATIONS (table-level correlations list) [{"col_a": "bmi", "col_b": "systolic_bp", "r": 0.41}] Enforced via Iman-Conover (rank reordering): preserves each column's marginal distribution while hitting the declared Pearson r exactly. Declare correlations for any pair of measurements that co-vary in the real domain (bmi/bp, income/spending, tenure/salary). Also supports full matrix syntax: correlations: matrix: columns: [hba1c, glucose, bmi] values: hba1c: [1.00, 0.65, 0.28] glucose: [0.65, 1.00, 0.22] bmi: [0.28, 0.22, 1.00]

ICC CLUSTER EFFECTS (parent table cluster_effect) cluster_effect: affects_table: visits affects_columns: hba1c: icc: 0.18 # intraclass correlation coefficient sd_total: 1.5 # total standard deviation; sd_between = sqrt(icc)*sd_total systolic_bp: sd_between: 8.0 # supply sd_between directly if preferred Applies per-parent-entity random intercepts to the named child columns. Required for multi-site or multi-centre designs — without it all sites look identical and any ICC statistical test will detect the synthetic origin. icc: 0.10-0.30 is typical for clinical measurements across sites.

STATE MACHINE (table-level state_machine) state_machine: state_column: patient_status initial_state: enrolled transitions: enrolled: {on_treatment: 0.97, screen_failure: 0.03} on_treatment: {completed: 0.77, dropout: 0.23} Assigns one terminal state to every row by following the Markov chain. States with no outgoing transitions are terminal. Use for any process with defined states: clinical trial statuses, customer lifecycle, order fulfilment stages, support ticket resolution.

SCHEMA-LEVEL DIRECTIVES (top-level keys, siblings of the tables)

outcome_curves Declare aggregate targets the engine hits EXACTLY. [{"table": "orders", "column": "amount", "time_column": "order_date", "time_unit": "month", "value_mode": "absolute", "start_date": "2024-01-01", "avg_transaction_value": 120.0, "curve_points": [ {"month": 1, "target_value": 50000.0}, {"month": 6, "target_value": 110000.0}, {"month": 12, "target_value": 200000.0} ]}] ALWAYS use this when the user states what a number should sum to per period: "revenue grows from $50k to $200k", "Q4 spike", "10x growth". avg_transaction_value drives row count per period; set it to roughly the median row value for that column.

rate_curves Per-period rate targets for boolean/categorical columns. [{"table": "transactions", "column": "is_fraud", "time_column": "transaction_date", "rate_points": [ {"period": "2024-01", "rate": 0.02}, {"period": "2024-Q4", "rate": 0.05} ]}] Use when fraud rate, churn rate, or conversion rate changes over time.

domain Domain hint for post-generation validation. "domain": "clinical_trial" # or "clinical", "financial", "fintech" After generating, call misata.validate_domain(tables, domain="clinical_trial") to surface any physiologically or financially impossible values. Built-in ranges: HbA1c 4-14 %, BMI 10-80, systolic BP 60-260, age 0-130, glucose 2-40, cholesterol 1-20, hemoglobin 3-25 for clinical; price ≥ 0, discount 0-1, rate -1 to 100 for financial.

DESIGN RULES — follow these to get the best result in one pass

1. Always set rows per table. A fintech schema with customers=2000, accounts=4000, transactions=50000 is far better than 1000 everywhere.

2. Every child table needs a FK column pointing to its parent PK. Without it orphan rows are generated and the integrity proof will fail.

3. Use lognormal for money, file sizes, response times (right-skewed, strictly positive). Use normal for measurements (height, score, temp).

4. Declare correlations for any pair that co-varies in the real domain. Generated data with an identity correlation matrix is the clearest synthetic-data tell there is.

5. Use exact_incidence instead of probability when the user states a precise rate. "3% fraud" with probability: 0.03 gives ~3% on average; exact_incidence gives exactly 3%.

6. Use rollup (not formula) for any parent column that must reconcile with child rows. customers.total_spent generated independently of orders will never match; a rollup makes it exact.

7. Use outcome_curves any time the user mentions a revenue shape, a growth trajectory, a seasonal pattern, or a specific period total. It is the single feature most likely to be forgotten and most visible when absent.

8. Use profiles when two groups need different distributions. A clinical trial where all arms share one HbA1c distribution is statistically wrong and the difference will be caught by any summary table.

9. For longitudinal data (visits, sessions, sensor readings), add time_series to the key measurement columns. Independent rows fail every autocorrelation test and are visually obvious when plotted.

10. Add state_machine to any entity that moves through a process. An order table with no status progression is not realistic order data.

Args: schema: Dict of table defs plus optional schema-level directives. rows: Default row count for tables without rows. seed: Random seed (same seed → byte-identical output on any machine). output_dir: Where to write CSVs. Omit to use a fresh temp dir. sample_rows: Rows per table to include in the JSON response (max 50).