Database Schema

The LightcurveDB schema is designed to efficiently store and retrieve astronomical time-series data from the TESS mission. The schema uses PostgreSQL with SQLAlchemy ORM, supporting complex relationships and polymorphic models.

Schema Overview

The database schema consists of several interconnected model groups:

1. Mission Hierarchy: Mission → MissionCatalog → Target

2. Instrument Hierarchy: Self-referential instrument tree

3. Observation System: Polymorphic observation models with FITS frame support

4. Processing Pipeline: PhotometricSource + DetrendingMethod → ProcessingGroup

5. Data Products: DataSet (lightcurves), TargetSpecificTime, and QualityFlagArray

Entity Relationship Diagram

        ---
config:
  theme: neutral
  layout: elk
  elk:
    mergeEdges: true
    nodePlacementStrategy: LINEAR_SEGMENTS
---
erDiagram
    Mission ||--o{ MissionCatalog : "has catalogs"
    MissionCatalog ||--o{ Target : "contains targets"

    Instrument ||--o{ Instrument : "parent/child"
    Instrument ||--o{ Observation : "produces"

    Observation ||--o{ FITSFrame : "polymorphic"
    Observation ||--o{ TargetSpecificTime : "has times"
    Observation ||--o{ DataSet : "has datasets"
    Observation ||--o{ QualityFlagArray : "has quality flags"

    Target ||--o{ TargetSpecificTime : "has times"
    Target ||--o{ DataSet : "has lightcurves"
    Target ||--o{ QualityFlagArray : "has quality flags"

    PhotometricSource ||--o{ ProcessingGroup : "used in"
    DetrendingMethod ||--o{ ProcessingGroup : "used in"
    ProcessingGroup ||--o{ DataSet : "produces"

    Mission {
        UUID id PK
        string name UK
        string description
        string time_unit
        decimal time_epoch
        string time_epoch_scale
        string time_epoch_format
        string time_format_name UK
    }

    MissionCatalog {
        int id PK
        UUID host_mission_id FK
        string name UK
        string description
    }

    Target {
        bigint id PK
        int catalog_id FK
        bigint name
    }

    Instrument {
        UUID id PK
        string name
        json properties
        UUID parent_id FK
    }

    Observation {
        int id PK
        string type
        array cadence_reference
        UUID instrument_id FK
    }

    FITSFrame {
        int id PK
        string type
        bigint cadence
        int observation_id FK
        bool simple
        int bitpix
        int naxis
        array naxis_values
        bool extended
        float bscale
        float bzero
        path file_path
    }

    PhotometricSource {
        int id PK
        string name UK
        string description
    }

    DetrendingMethod {
        int id PK
        string name UK
        string description
    }

    ProcessingGroup {
        int id PK
        string name
        string description
        int photometric_source_id FK
        int detrending_method_id FK
    }

    DataSet {
        int id PK
        int processing_group_id FK
        int target_id FK
        int observation_id FK
        array values
        array errors
    }

    TargetSpecificTime {
        bigint id PK
        int target_id FK
        int observation_id FK
        array barycentric_julian_dates
    }

    QualityFlagArray {
        bigint id PK
        string type
        int observation_id FK
        int target_id FK
        array quality_flags
        datetime created_on
    }
    

LightcurveDB Entity Relationship Diagram

Model Descriptions

Mission Models

class lightcurvedb.models.Mission(**kwargs)

Bases: LCDBModel, NameAndDescriptionMixin, CreatedOnMixin

Represents a space mission or survey program.

A Mission defines the top-level context for astronomical observations, including time system definitions and associated catalogs. Examples include TESS (Transiting Exoplanet Survey Satellite).

id

Unique identifier for the mission

Type:

UUID

name

Unique name of the mission (e.g., “TESS”)

Type:

str

description

Detailed description of the mission

Type:

str

time_unit

Unit of time measurement (e.g., “day”)

Type:

str

time_epoch

Reference epoch for time calculations

Type:

Decimal

time_epoch_scale

Time scale for the epoch (e.g., “tdb”)

Type:

str

time_epoch_format

Format of the epoch specification

Type:

str

time_format_name

Unique name for the mission’s time format

Type:

str

catalogs

Associated catalogs for this mission

Type:

list[MissionCatalog]

Examples

>>> mission = Mission(name="TESS",
...                   description="Transiting Exoplanet Survey Satellite")

created_on: orm.Mapped[datetime.datetime]

name: orm.Mapped[str]

class lightcurvedb.models.MissionCatalog(**kwargs)

Bases: LCDBModel, NameAndDescriptionMixin, CreatedOnMixin

A catalog of astronomical targets associated with a mission.

MissionCatalog represents a specific catalog within a mission context, such as the TESS Input Catalog (TIC). It serves as a container for organizing targets observed by the mission.

id

Primary key identifier

Type:

int

host_mission_id

Foreign key to the parent Mission

Type:

UUID

name

Unique catalog name (e.g., “TIC” for TESS Input Catalog)

Type:

str

description

Detailed description of the catalog

Type:

str, optional

host_mission

Parent mission this catalog belongs to

Type:

Mission

targets

Collection of targets in this catalog

Type:

list[Target]

created_on: orm.Mapped[datetime.datetime]

name: orm.Mapped[str]

class lightcurvedb.models.Target(**kwargs)

Bases: LCDBModel

An astronomical target (star, planet, etc.) in a mission catalog.

Target represents an individual astronomical object that is observed during a mission. Each target is uniquely identified within its catalog by a numeric identifier (e.g., TIC ID for TESS targets).

id

Primary key identifier

Type:

int

catalog_id

Foreign key to the MissionCatalog

Type:

int

name

Catalog-specific identifier (e.g., TIC ID)

Type:

int

catalog

The catalog this target belongs to

Type:

MissionCatalog

datasets

Processed lightcurve datasets for this target

Type:

list[DataSet]

target_specific_times

Time series specific to this target

Type:

list[TargetSpecificTime]

quality_flag_arrays

Target-specific quality flags

Type:

list[QualityFlagArray]

Notes

The combination of catalog_id and name must be unique, ensuring no duplicate targets within a catalog.

Instrument Model

class lightcurvedb.models.Instrument(**kwargs)

Bases: LCDBModel

Represents a scientific instrument or assembly used for observations.

Instruments form a hierarchical structure where an instrument can be either a physical device (e.g., a CCD) or an assembly containing other instruments (e.g., a camera with multiple CCDs). This allows modeling complex instrument configurations.

id

Unique identifier for the instrument

Type:

UUID

name

Name of the instrument (e.g., “Camera 1”, “CCD 2”)

Type:

str

properties

JSON dictionary of instrument-specific properties and metadata

Type:

dict

parent_id

Foreign key to parent instrument (None for top-level instruments)

Type:

UUID, optional

parent

Parent instrument in the hierarchy

Type:

Instrument, optional

children

Child instruments if this is an assembly

Type:

list[Instrument]

observations

Observations made using this instrument

Type:

list[Observation]

Examples

>>> camera = Instrument(name="TESS Camera 1")
>>> ccd = Instrument(name="CCD 1", parent=camera)

Notes

The self-referential relationship allows building instrument trees of arbitrary depth, useful for complex telescope configurations.

Observation Models

class lightcurvedb.models.Observation(**kwargs)

Bases: LCDBModel

Base class for astronomical observations.

Observation is a polymorphic base class that represents a collection of measurements taken by an instrument. Subclasses can specialize this for different observation types while maintaining a common interface.

This design allows mission-specific observations (e.g., TESSObservation, HSTObservation) to extend the base model with mission-specific fields while sharing common functionality.

id

Primary key identifier

Type:

int

type

Polymorphic discriminator for subclass type

Type:

str

cadence_reference

Array of cadence numbers for time ordering

Type:

ndarray[int64]

instrument_id

Foreign key to the instrument used

Type:

uuid.UUID

instrument

The instrument that made this observation

Type:

Instrument

datasets

Processed versions of this observation

Type:

list[DataSet]

target_specific_times

Target-specific time corrections

Type:

list[TargetSpecificTime]

Examples

Creating a mission-specific observation subclass:

>>> class TESSObservation(Observation):
...     __mapper_args__ = {
...         "polymorphic_identity": "tess_observation",
...     }
...     sector: Mapped[int]
...     orbit_number: Mapped[int]

Notes

This is a polymorphic base class using single table inheritance. The ‘type’ field determines the specific observation subclass. Mission-specific fields should be added via subclassing, not by modifying this base class.

class lightcurvedb.models.TargetSpecificTime(**kwargs)

Bases: LCDBModel

Time series data specific to a target-observation pair.

This model stores barycentric-corrected time values that account for the specific position of a target. It serves as a junction between Target and Observation with additional time data.

id

Primary key identifier

Type:

int

target_id

Foreign key to the target

Type:

int

observation_id

Foreign key to the observation

Type:

int

barycentric_julian_dates

Array of barycentric Julian dates corrected for target position

Type:

ndarray[float64]

target

The astronomical target

Type:

Target

observation

The observation these times correspond to

Type:

Observation

Notes

Barycentric correction accounts for Earth’s motion around the solar system barycenter, providing consistent timing for astronomical observations.

Frame Models

class lightcurvedb.models.FITSFrame(**kwargs)

Bases: LCDBModel, CreatedOnMixin

Represents a FITS (Flexible Image Transport System) frame.

FITSFrame stores metadata about individual FITS files used in astronomical observations. It uses polymorphic inheritance to support different frame types while maintaining FITS standard compliance.

id

Primary key identifier

Type:

int

type

Polymorphic discriminator for frame type

Type:

str

cadence

Time-ordered frame number

Type:

int

observation_id

Foreign key to parent observation

Type:

int

simple

FITS primary keyword - file conforms to FITS standard

Type:

bool

bitpix

FITS primary keyword - bits per pixel

Type:

int

naxis

FITS primary keyword - number of axes

Type:

int

naxis_values

Array representation of NAXIS1, NAXIS2, etc.

Type:

list[int]

extended

FITS primary keyword - file may contain extensions

Type:

bool

bscale

Linear scaling factor (physical = bzero + bscale * stored)

Type:

float

bzero

Zero point offset for scaling

Type:

float

file_path

File system path to the FITS file

Type:

Path, optional

Notes

The type-cadence combination must be unique, enforced by database constraint. Polymorphic on ‘type’ field allows for specialized frame subclasses.

created_on: orm.Mapped[datetime.datetime]

Processing Models

class lightcurvedb.models.PhotometricSource(**kwargs)

Bases: LCDBModel, NameAndDescriptionMixin

Defines a source or method of photometric measurement.

PhotometricSource represents different ways of extracting photometric data from observations, such as aperture photometry with different aperture sizes or PSF photometry.

id

Primary key identifier

Type:

int

name

Name of the photometric method (inherited from mixin)

Type:

str

description

Detailed description (inherited from mixin)

Type:

str

processing_groups

Processing groups using this photometric source

Type:

list[ProcessingGroup]

Examples

>>> aperture_2px = PhotometricSource(name="Aperture_2px",
...                                  description="2 pixel radius aperture")

name: orm.Mapped[str]

class lightcurvedb.models.DetrendingMethod(**kwargs)

Bases: LCDBModel, NameAndDescriptionMixin

Represents a method for removing systematic trends from lightcurves.

DetrendingMethod defines algorithms used to remove instrumental or systematic effects from photometric time series, such as PDC-SAP (Pre-search Data Conditioning Simple Aperture Photometry).

id

Primary key identifier

Type:

int

name

Name of the detrending method (inherited from mixin)

Type:

str

description

Detailed description (inherited from mixin)

Type:

str

processing_groups

Processing groups using this detrending method

Type:

list[ProcessingGroup]

Examples

>>> pdc = DetrendingMethod(name="PDC-SAP",
...                        description="Pre-search Data Conditioning")

name: orm.Mapped[str]

class lightcurvedb.models.ProcessingGroup(**kwargs)

Bases: LCDBModel, NameAndDescriptionMixin

Combines a photometric source with a detrending method.

ProcessingGroup represents a unique combination of how photometry was extracted and how it was detrended. This allows tracking different processing pipelines applied to the same observations.

id

Primary key identifier

Type:

int

name

Name of the processing group (inherited from mixin)

Type:

str

description

Detailed description (inherited from mixin)

Type:

str

photometric_source_id

Foreign key to photometric source

Type:

int

detrending_method_id

Foreign key to detrending method

Type:

int

photometric_source

The photometric extraction method

Type:

PhotometricSource

detrending_method

The detrending algorithm

Type:

DetrendingMethod

datasets

Lightcurve datasets using this processing

Type:

list[DataSet]

Notes

The combination of photometric_source_id and detrending_method_id must be unique, ensuring no duplicate processing groups.

name: orm.Mapped[str]

class lightcurvedb.models.DataSet(**kwargs)

Bases: LCDBModel

A processed lightcurve for a specific target and observation.

DataSet is the central model that connects a target, an observation, and a processing method to produce a final lightcurve. It stores the actual photometric measurements and uncertainties.

id

Primary key identifier

Type:

int

processing_group_id

Foreign key to processing group

Type:

int

target_id

Foreign key to target

Type:

int

observation_id

Foreign key to observation

Type:

int

values

Array of photometric measurements (flux or magnitude)

Type:

ndarray[float64]

errors

Array of measurement uncertainties

Type:

ndarray[float64], optional

processing_group

The processing method used

Type:

ProcessingGroup

target

The astronomical target

Type:

Target

observation

The source observation

Type:

Observation

Notes

This is the main table for storing lightcurve data. Each row represents one complete lightcurve for a target processed with a specific method.

Quality Flag Model

class lightcurvedb.models.QualityFlagArray(**kwargs)

Bases: LCDBModel, CreatedOnMixin

Stores quality flag arrays for astronomical observations.

QualityFlagArray represents bit-encoded quality information for time-series astronomical data. Each element in the array corresponds to a cadence in the observation, with individual bits representing different quality conditions or data issues.

This is a polymorphic base class that can be extended for mission-specific quality flag implementations with specialized bit definitions.

Parameters:

• type (str) – Quality flag type identifier (e.g., ‘pixel_quality’, ‘cosmic_ray’)

• observation_id (int) – Foreign key to the parent observation

• target_id (int, optional) – Foreign key to a specific target when flags are target-specific

• quality_flags (ndarray[int32]) – Array of 32-bit integers where each bit represents a quality condition

id

Primary key identifier

Type:

int

type

Polymorphic discriminator and quality flag category

Type:

str

observation_id

Reference to the parent observation

Type:

int

target_id

Reference to specific target (null for observation-wide flags)

Type:

int or None

quality_flags

Bit-encoded quality flag array

Type:

ndarray[int32]

observation

Parent observation relationship

Type:

Observation

target

Target relationship when flags are target-specific

Type:

Target or None

created_on

Timestamp of record creation (from CreatedOnMixin)

Type:

datetime

Examples

Creating observation-wide quality flags:

>>> obs_flags = QualityFlagArray(
...     observation_id=12345,
...     quality_flags=np.array([0, 1, 4, 5], dtype=np.int32)
... )

Creating target-specific quality flags:

>>> target_flags = QualityFlagArray(
...     observation_id=12345,
...     target_id=67890,
...     quality_flags=np.array([0, 0, 2, 8], dtype=np.int32)
... )

Interpreting bit flags:

>>> # Bit 0: Cosmic ray
>>> # Bit 1: Saturation
>>> # Bit 2: Bad pixel
>>> cosmic_ray_mask = (flags.quality_flags & 1) != 0
>>> saturated_mask = (flags.quality_flags & 2) != 0

Extending with single-table inheritance (simple approach):

>>> class TESSQualityFlags(QualityFlagArray):
...     """TESS-specific quality flags with known bit definitions."""
...     __mapper_args__ = {
...         "polymorphic_identity": "tess_quality",
...     }
...     @property
...     def cosmic_ray_events(self):
...         """Return mask of cosmic ray events (bit 0)."""
...         flags = np.array(self.quality_flags, dtype=np.int32)
...         return (flags & 1) != 0
...     @property
...     def saturated_pixels(self):
...         """Return mask of saturated pixels (bit 1)."""
...         flags = np.array(self.quality_flags, dtype=np.int32)
...         return (flags & 2) != 0
...     @property
...     def spacecraft_anomaly(self):
...         """Return mask of spacecraft anomalies (bit 4)."""
...         flags = np.array(self.quality_flags, dtype=np.int32)
...         return (flags & 16) != 0

Extending with joined-table inheritance (advanced approach):

class SpectroscopicQualityFlags(QualityFlagArray):
    """Quality flags for spectroscopic observations."""

    __tablename__ = "spectroscopic_quality_flags"
    __mapper_args__ = {
        "polymorphic_identity": "spectroscopic_quality",
    }

    # Primary key also serves as foreign key to parent table
    id = orm.mapped_column(
        sa.ForeignKey("quality_flag_array.id"), primary_key=True
    )

    # Additional columns specific to spectroscopic data
    wavelength_calibration_quality = orm.mapped_column(
        sa.types.Float,
        comment="Wavelength calibration quality score (0-1)"
    )
    spectral_resolution = orm.mapped_column(
        sa.types.Float,
        comment="Actual spectral resolution achieved"
    )
    calibration_lamp_id = orm.mapped_column(
        sa.ForeignKey("calibration_lamp.id"), nullable=True
    )

    @property
    def wavelength_drift(self):
        """Return mask of wavelength drift (bit 8)."""
        flags = np.array(self.quality_flags, dtype=np.int32)
        return (flags & 256) != 0

class PhotometricQualityFlags(QualityFlagArray):
    """Quality flags for photometric observations."""

    __tablename__ = "photometric_quality_flags"
    __mapper_args__ = {
        "polymorphic_identity": "photometric_quality",
    }

    id = orm.mapped_column(
        sa.ForeignKey("quality_flag_array.id"), primary_key=True
    )

    # Photometry-specific metadata
    sky_background_level = orm.mapped_column(
        sa.types.Float,
        comment="Median sky background in counts"
    )
    fwhm = orm.mapped_column(
        sa.types.Float,
        comment="Full width at half maximum of PSF"
    )
    extinction_coefficient = orm.mapped_column(
        sa.types.Float, nullable=True
    )

Polymorphic querying examples:

>>> # Query all quality flags for an observation
>>> all_flags = session.query(QualityFlagArray).filter_by(
...     observation_id=12345
... ).all()

>>> # Query only TESS quality flags
>>> tess_flags = session.query(TESSQualityFlags).filter_by(
...     observation_id=12345
... ).all()

>>> # Use with_polymorphic for efficient joined loading
>>> from sqlalchemy.orm import with_polymorphic
>>>
>>> poly_flags = with_polymorphic(
...     QualityFlagArray,
...     [SpectroscopicQualityFlags, PhotometricQualityFlags]
... )
>>> query = session.query(poly_flags).filter(
...     poly_flags.observation_id == 12345
... )
>>>
>>> # Access subclass-specific attributes without additional queries
>>> for flag in query:
...     if isinstance(flag, SpectroscopicQualityFlags):
...         print(f"Spectral resolution: {flag.spectral_resolution}")
...     elif isinstance(flag, PhotometricQualityFlags):
...         print(f"Sky background: {flag.sky_background_level}")

>>> # Filter by polymorphic type
>>> spectro_only = session.query(QualityFlagArray).filter_by(
...     type="spectroscopic_quality"
... ).all()

Notes

The combination of (type, observation_id, target_id) must be unique, preventing duplicate quality flag arrays for the same context. NULL values in target_id are treated as equal, so only one observation-wide quality flag array (with NULL target_id) is allowed per type and observation_id combination.

Quality flag bit definitions are mission and type-specific. Subclasses should document their specific bit meanings and may add helper methods for flag interpretation.

See also

Observation

Parent observation model

Target

Associated target for target-specific flags

created_on: orm.Mapped[datetime.datetime]

Polymorphic Models

The schema uses SQLAlchemy’s polymorphic inheritance for flexibility:

1. Observation: Base class with polymorphic_on=”type”

   • Allows different observation types to share common attributes

   • Subclasses can add specialized fields while maintaining relationships

2. FITSFrame: Configured for polymorphism with polymorphic_on=”type”

   • Supports different FITS frame types (e.g., science frames, calibration frames)

   • Identity “basefits” serves as the default type

3. QualityFlagArray: Base class with polymorphic_on=”type”

   • Enables mission-specific quality flag implementations

   • Identity “base_quality_flag” serves as the default type

   • Can be extended to add mission-specific bit interpretations

Mission-Specific Extensions

LightcurveDB supports mission-specific data through SQLAlchemy’s polymorphic inheritance. The Observation model serves as a base class that can be extended for specific missions.

Design Pattern

To add support for a new mission:

1. Create a subclass of Observation

2. Set a unique polymorphic_identity

3. Add mission-specific fields as Mapped columns

4. Register in your mission’s module

Example: TESS Observations

from lightcurvedb.models import Observation
from sqlalchemy import orm

class TESSObservation(Observation):
    """TESS-specific observation with orbit and sector information."""

    __mapper_args__ = {
        "polymorphic_identity": "tess_observation",
    }

    # TESS-specific fields
    sector: orm.Mapped[int]
    orbit_number: orm.Mapped[int]
    spacecraft_quaternion: orm.Mapped[dict]  # Store as JSON
    cosmic_ray_mitigation: orm.Mapped[bool]

Example: HST Observations

class HSTObservation(Observation):
    """Hubble Space Telescope observation with visit information."""

    __mapper_args__ = {
        "polymorphic_identity": "hst_observation",
    }

    visit_id: orm.Mapped[str]
    program_id: orm.Mapped[int]
    filter_name: orm.Mapped[str]
    exposure_time: orm.Mapped[float]

Querying Mission-Specific Data

# Query all observations (any mission)
all_obs = session.query(Observation).all()

# Query only TESS observations
tess_obs = session.query(TESSObservation).filter_by(sector=1).all()

# Polymorphic loading - automatically returns correct subclass
obs = session.query(Observation).first()
if isinstance(obs, TESSObservation):
    print(f"TESS Sector: {obs.sector}")

Benefits

• Type Safety: Mission-specific fields are properly typed

• Clean Schema: No unused fields for other missions

• Extensibility: New missions don’t require schema changes

• Performance: Single table inheritance is efficient

• Flexibility: Can query all observations or mission-specific ones

Key Relationships

One-to-Many:

• Mission → MissionCatalog → Target (hierarchical)

• Instrument → Observation

• ProcessingGroup → DataSet

• Observation → QualityFlagArray

• Target → QualityFlagArray (optional relationship)

Many-to-Many (via junction tables):

• Target ↔ Observation (via TargetSpecificTime)

• PhotometricSource + DetrendingMethod → ProcessingGroup

Self-Referential:

• Instrument parent/child hierarchy for complex instrument configurations

Central Hub:

• DataSet connects Target + Observation + ProcessingGroup

• This is where the actual lightcurve data resides

Usage Examples

Querying for a target’s lightcurves:

from lightcurvedb.models import Target, DataSet

# Get all lightcurves for a specific TIC ID
target = session.query(Target).filter_by(name=12345678).first()
lightcurves = target.datasets

# Get lightcurves with specific processing
for lc in lightcurves:
    print(f"Processing: {lc.processing_group.name}")
    print(f"Values: {lc.values}")

Creating instrument hierarchy:

from lightcurvedb.models import Instrument

# Create camera with CCDs
camera = Instrument(name="TESS Camera 1")
ccd1 = Instrument(name="CCD 1", parent=camera)
ccd2 = Instrument(name="CCD 2", parent=camera)

session.add_all([camera, ccd1, ccd2])

Working with quality flags:

from lightcurvedb.models import QualityFlagArray, Target, Observation
import numpy as np

# Get quality flags for a specific target observation
target = session.query(Target).filter_by(name=12345678).first()
observation = target.observations[0]

# Get quality flags for this target in this observation
quality_flags = session.query(QualityFlagArray).filter_by(
    observation=observation,
    target=target,
    type="base_quality_flag"
).first()

if quality_flags:
    # Check for cosmic ray events (bit 0)
    cosmic_ray_mask = (quality_flags.quality_flags & 1) != 0
    num_cosmic_rays = np.sum(cosmic_ray_mask)
    print(f"Found {num_cosmic_rays} cadences with cosmic ray events")

    # Check for saturated pixels (bit 1)
    saturation_mask = (quality_flags.quality_flags & 2) != 0
    print(f"Saturated in {np.sum(saturation_mask)} cadences")

Database Constraints

The schema enforces several important constraints:

1. Unique Constraints:

   • Mission.name must be unique

   • MissionCatalog.name must be unique

   • Target: (catalog_id, name) combination must be unique

   • ProcessingGroup: (photometric_source_id, detrending_method_id) must be unique

   • FITSFrame: (type, cadence) combination must be unique

   • QualityFlagArray: (type, observation_id, target_id) must be unique (with NULL handling)

2. Cascade Deletes:

   • Deleting an Observation cascades to FITSFrame, TargetSpecificTime, DataSet, and QualityFlagArray

   • Deleting a ProcessingGroup cascades to DataSet

   • Deleting a Target cascades to DataSet

3. Referential Integrity:

   • All foreign keys are enforced at the database level

   • Orphaned records are prevented through proper relationships