BUSACT702 · Accounting Information Systems
Databases & Data Modelling
University of Auckland BUSACT 702 turns from process pictures to the data underneath them: the relational database model, entity-relationship (ER) diagrams, reading cardinalities and writing relationship sentences in both directions. The examinable skill is to read a set of cardinalities and translate them into the business rules they enforce — for example, whether partial picks, partial shipments or partial invoices are allowed — which also feeds the Power BI data-analytics work.
What this chapter covers
- 01The relational model: data held in related tables (entities) rather than in one flat file; keys link them
- 02Entity-relationship (ER) diagram: entities (e.g. Customer, Sales order, Stock picking, Shipment, Sales invoice) connected by relationships
- 03Cardinality: whether a relationship is one-to-one, one-to-many (1:N) or many-to-many, in each direction
- 04Relationship sentences: stating a relationship in both directions ('one customer places many orders; an order relates to one customer')
- 05Translating cardinalities into business rules: partial picks allowed vs partial shipments not allowed vs invoiced in full
- 06Why a good data model supports the AIS: consistent, non-redundant data that controls and analytics can rely on
- 07How ER modelling feeds Power BI: the model you connect and relate is the analytics foundation
Reading cardinalities into business rules
- +1(a) Partial picks — ALLOWED. A Sales order triggers many Stock pickings (1:N). Because one order can generate several pickings, the business can pick part of an order now and go back to pick the rest later — that is exactly a partial pick.
- +1(b) Partial shipments — NOT allowed. A Stock picking relates to one Shipment only. Since a picking cannot be split across shipments, you cannot part-ship a picking; each picking goes out whole in a single shipment.
- +1(c) Partial invoicing — NOT allowed (invoiced in full). A Shipment is billed on one Sales invoice. A shipment cannot be spread across several invoices, so it is invoiced in full; allowing partial invoicing would require changing that relationship to many.
Key terms
- Relational model
- A way of storing data in related tables (entities) linked by keys, avoiding the redundancy and inconsistency of one flat file — the foundation of a modern AIS database.
- Entity
- A thing the business stores data about (Customer, Sales order, Shipment); it becomes a table, with attributes as columns.
- Entity-relationship (ER) diagram
- A diagram of entities and the relationships between them, annotated with cardinalities; it models the data structure a business process relies on.
- Cardinality
- How many instances of one entity relate to another in each direction — one-to-one, one-to-many (1:N) or many-to-many. It encodes the business rules.
- Relationship sentence
- A plain-English statement of a relationship in one direction (e.g. 'a sales order relates to exactly one customer'); writing both directions makes the cardinality explicit.
- One-to-many (1:N)
- A relationship where one instance of an entity links to many of another (one customer, many orders). Reading which side is 'one' tells you whether an activity can be split (partial picks/shipments/invoices).
Databases & Data Modelling FAQ
What is an ER diagram and why does the course use it?
It models the data behind a process — the entities (Customer, Order, Shipment...) and how they relate, with cardinalities. It matters because the cardinalities encode business rules, and a clean data model is what the AIS and its analytics rely on.
How do I turn cardinalities into business rules?
Read the 'one' side. If a child entity relates to exactly one parent, it cannot be split, so partials are not allowed; a one-to-many from the parent is what permits partials (many pickings per order = partial picks allowed).
What are relationship sentences?
Plain-English statements of a relationship in both directions — 'one customer places many orders; an order relates to one customer'. Writing both directions forces you to state the cardinality precisely, which is the marked skill.
How does data modelling connect to Power BI?
The entities and relationships you model are the data you then connect, relate and visualise in Power BI. A sound model makes the analytics reliable; a redundant or inconsistent one produces misleading dashboards.
Exam move
Practise the two-way reading of an ER diagram: for every relationship write both sentences, note the cardinality, then translate it into a business rule. Drill the partial-picks / partial-shipments / partial-invoices question until reading the 'one' side is automatic — that is the examinable move. Keep the link to analytics in mind: the model you can read is the model you can build in Power BI. Confirm on Canvas how much database/ER content your quarter assesses versus flowcharting and controls.
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