| Course | BU 453 Database Management |
|---|---|
| Unit | Unit 2 |
| Paper type | Entity relationship diagram |
| Length | About 700 words, 5 pages |
| Format | APA 7 student paper |
| School | Herzing University |
| Program | BS in Business Analytics |
| Updated | September 2026 |
Free sample paper for BU 453 Unit 2
Twelve Relationships, Each Read Both Ways With Its Reason: An Entity Relationship Diagram and Register for a Composite Boise Music School
Student Name
Business, Herzing University
BU 453: Database Management
Instructor Name
January 28, 2026
Twelve Relationships, Each Read Both Ways With Its Reason: An Entity Relationship Diagram and Register for a Composite Boise Music School
From Entities to Relationships
The requirements exercise for Harmony Hill Music School, a composite Boise lesson school, identified ten record types from the owner's narrative. This unit connects them. The diagram uses crow's foot notation, in which each end of a relationship line shows the minimum and maximum number of records that can take part: a bar for one, a circle for zero and a crow's foot for many. Because the drawing cannot be reproduced here in full, its content is set out in a relationship register, which is the part of the work that matters most. Each relationship is named with a verb phrase readable in both directions, given its cardinality and optionality on each side, and tied to the sentence in the owner's narrative, numbered S1 to S10, that fixed it.
Chen (1976) defined relationships as associations among entities and showed that their cardinality is a fact about the organization, not a design preference. Every cardinality below is therefore justified by what the school does, and where the narrative is silent, the choice is marked as an assumption.
The Relationship Register
Cardinality is written as minimum and maximum on each side; for example, 0..many means optional and many, 1..1 means mandatory and exactly one.
| No. | Reads as | And back | Left side | Right side | Why |
|---|---|---|---|---|---|
| R1 | A billing account pays for students | A student is paid for by one billing account | Account 1..many students | Student 1..1 account | S5: families billed once; every student is billed somewhere |
| R2 | A guardian is a contact for students | A student has guardians as contacts | Guardian 1..many | Student 0..many | S4: minors need one or two; adults need none; one guardian may have several children |
| R3 | A student holds enrollments | An enrollment belongs to one student | Student 0..many | Enrollment 1..1 | S2: one or two instruments; a returning student may have none between terms |
| R4 | A teacher teaches enrollments | An enrollment is taught by one teacher | Teacher 0..many | Enrollment 1..1 | S2: one teacher per lesson; a new teacher may have none yet |
| R5 | A room hosts enrollments | An enrollment meets in one room | Room 0..many | Enrollment 1..1 | S2: one of nine rooms |
| R6 | A term contains enrollments | An enrollment runs for one term | Term 0..many | Enrollment 1..1 | S2, S3 |
| R7 | An enrollment produces lessons | A lesson belongs to one enrollment | Enrollment 0..many | Lesson 1..1 | S8: each week's lesson recorded |
| R8 | An instrument is out on rentals | A rental is of one instrument | Instrument 0..many | Rental 1..1 | S6, S7: many rentals over the years |
| R9 | A student takes rentals | A rental is to one student | Student 0..many | Rental 1..1 | S6 |
| R10 | A recital features performances | A performance is in one recital | Recital 1..many | Performance 1..1 | S9 |
| R11 | A student gives performances | A performance is given by one student | Student 0..many | Performance 1..1 | S9; teachers do not perform (assumption) |
| R12 | A billing account receives invoices; an invoice is settled by payments | An invoice goes to one account; a payment settles one invoice | Account 0..many invoices; invoice 0..many payments | Invoice 1..1 account; payment 1..1 invoice | S5; payments assumed |
Reading each relationship aloud in both directions caught two errors in the first draft. R2 was drawn as one guardian to many students, which read correctly one way, but read backward it said a student could have only one guardian, contradicting S4. And R8 first allowed an instrument at most one rental, which read backward meant an instrument could never be rented a second time, contradicting S7's many rentals over the years. Both mistakes would have passed a glance at the drawing, because a line with a crow's foot at one end looks plausible either way round; only the sentence read aloud exposed them.
Resolving the Many-to-Many Relationships
Three relationships are many-to-many at the conceptual level, and each is resolved now with an associative entity that carries its own facts.
Student and guardian (R2) are many-to-many: a child may have two guardians and a guardian several children. The associative entity Student Guardian holds one row per pairing, with the guardian's relationship to that child and a flag for the primary contact, facts that belong to the pairing rather than to either person. Student and instrument are many-to-many over time: a student may rent several instruments in succession, and an instrument is rented by many students over the years. Rental resolves it, holding the start date, end date and monthly fee agreed. Student and recital are many-to-many: a student may perform in several recitals, and a recital has many performers. Performance resolves it, holding the piece, the composer and the running order.
Resolving these now, rather than leaving them for the schema, matters because the facts they carry, such as a rental's dates, have nowhere to live in a plain many-to-many line. Hoffer et al. (2019) note that an associative entity is justified when the relationship itself has attributes, and all three here do.
What Cardinality Cannot Express
Some business rules are stronger than cardinality can show. S7 says an instrument is rented to only one student at a time. The diagram shows that an instrument can have many rentals, which is true over time, but it cannot say that those rentals must not overlap in dates. S4 says students under 18 need a guardian; the diagram shows guardians as optional for students, because adults need none, but it cannot express that the rule depends on age. And S2 implies two lessons cannot be in the same room at the same time. These rules are recorded in the register as constraints to be implemented in the schema and tested in the integrity unit. Connolly and Begg (2015) describe such rules as enterprise constraints, which the data model must document even when its notation cannot draw them. Harmony Hill, its narrative and its twelve relationships are invented for this course, and the owner's answers to the open assumptions would be sought before the schema is built.
References
Chen, P. P.-S. (1976). The entity-relationship model: Toward a unified view of data. ACM Transactions on Database Systems, 1(1), 9-36. https://doi.org/10.1145/320434.320440
Connolly, T., & Begg, C. (2015). Database systems: A practical approach to design, implementation, and management (6th ed.). Pearson.
Hoffer, J. A., Ramesh, V., & Topi, H. (2019). Modern database management (13th ed.). Pearson.
What the BU 453 Unit 2 instructions ask for
In the second unit, BU 453 asks students to draw an entity relationship diagram for the scenario modeled in Unit 1. Common requirements include a named notation, every relationship labeled, cardinality and optionality shown at both ends, justification for each from the scenario, and treatment of many-to-many relationships. Many instructors ask whether many-to-many relationships must be resolved at this stage; resolving them when the relationship carries its own facts is usually expected. Students should note business rules the diagram cannot express. Most submissions pair the diagram with a relationship register and APA 7 discussion; the strongest show how reading relationships aloud caught mistakes in the first draft.
How this BU 453 Unit 2 example is built
The paper opens by explaining crow's foot notation and why the register carries the argument. A twelve-row register names each relationship in both directions, states cardinality on each side and cites the justifying sentence. A paragraph describes two errors caught by reading relationships backward. A section resolves three many-to-many relationships, student and guardian, student and instrument, and student and recital, into associative entities with their own attributes, citing guidance on when such entities are justified. The final section lists business rules that cardinality cannot express, including non-overlapping rentals and age-dependent guardian requirements, and carries them forward as constraints for the schema and integrity units. Each resolved entity is shown with its composite identifier, so the step from diagram to tables in later units is already visible.
BU 453 Unit 2 rubric: what full points look like
ERD rubrics usually reward correct notation, complete relationships, accurate cardinality and optionality, justification from the scenario, proper handling of many-to-many relationships and recognition of rules beyond the diagram, plus presentation. Notation earns full credit when it is named and used consistently. Completeness scores highest when every needed connection appears. Cardinality is judged on whether both ends are correct and defensible. Justification rewards citing the scenario for each choice. Many-to-many handling earns points when associative entities carry the facts that belong to the pairing. Instructors also credit students who list constraints the notation cannot show, since those rules otherwise disappear before implementation.
Common BU 453 Unit 2 mistakes, and how to avoid them
Relationship diagrams commonly lose points when relationships are unnamed lines, leaving readers to guess what they mean. Another frequent problem is cardinality shown at only one end, or reversed so it reads wrongly in one direction. Students often leave many-to-many relationships unresolved even when the pairing has its own facts, such as a rental's dates. Some make every relationship mandatory, ignoring new records that have no partners yet. Others draw relationships the scenario never mentions. Many diagrams omit business rules that cardinality cannot express, which then never reach the schema. Finally, diagramming a company's real data model can disclose proprietary design; the assigned scenario demonstrates the same skill safely.
Get a BU 453 Unit 2 example written to your instructions
Drop in the Unit 2 brief, the rubric your section uses, the scenario and whatever entity list you produced earlier, plus any diagramming tool BU 453 requires. The custom example states each relationship in words from both ends, separates cardinality from optionality, keeps the earlier names and declares one notation. First one free, returned in 24 to 48 hours.
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BU 453 Unit 2 questions, answered
Which notation should the diagram use?
The one your section teaches, and the instructions will say. Crow's foot is common in business courses and chen style appears in others, and both express the same facts differently. What matters is declaring the choice on the page and holding it, because a marker checking cardinality against a symbol from another convention will read your model as saying something you did not mean.
Do many-to-many relationships have to be resolved now?
Usually not in this unit, and flagging one is better than quietly leaving it. A conceptual diagram is allowed to show the relationship as the business describes it, with a register note saying it will need its own entity when the model is implemented and naming the facts that entity would carry. Where the instructions ask for a logical model, resolve it and show both.
My company has a data model. Can I diagram that one?
A schema is a design document, and designs are among the things organizations most reliably treat as their own. Drawing an internal model for a school assignment publishes how the business stores what it knows, including things about customers that were never yours to describe. Model the case in the assignment; if it seems thin next to what you see at work, say so in the assumptions.
Where can I find a free BU 453 Unit 2 sample paper?
A full BU 453 Unit 2 entity relationship diagram and register can be read here without charge, including all twelve relationships and margin notes. For your own scenario's diagram, forward the prompt and we write a matching register free, usually inside 48 hours.
Do many-to-many relationships need resolving in BU 453 Unit 2?
When the pairing has facts of its own, yes. The sample resolves three, because rentals carry dates, performances carry pieces and guardian pairings carry the relationship and primary-contact flag.