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CS 101 – Nov. 9

CS 101 – Nov. 9. Text software issues (continued) Readability Fonts Database concepts Relationships Queries. Readability. First, need to measure: Words per sentence Syllables per word How to Write Plain English by Flesch: 206.835 – 84.6*spw– 1.015*wps 90’s = fifth grade

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CS 101 – Nov. 9

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  1. CS 101 – Nov. 9 Text software issues (continued) • Readability • Fonts • Database concepts • Relationships • Queries

  2. Readability • First, need to measure: • Words per sentence • Syllables per word • How to Write Plain English by Flesch: 206.835 – 84.6*spw– 1.015*wps 90’s = fifth grade 30’s = college level

  3. Fonts • Font = style of printing • Typeface • Point size • Ex. Times 10, Helvetica 12 • Fonts can be distinguished by • Sarif or sans sarif • Proportional or non-proportional

  4. Font types • Sarif = has feet • Sans sarif = no feet • Look at: i, h, n, r, … (but not t!) • Proportional = width of characters changes • Non-proportional = all have same width

  5. Access review • Purpose: Manage data • Parts of a database • If your database has only 1 table, you are better off using Excel • Relationship between tables? • None • One-to-one • One-to-many (most common) • Many-to-many

  6. Table design • What fields to we need? • Age?  store birth date • GPA?  store credits and quality points • What year?  store date of admission • Store data in its smallest parts (e.g. address) • Calculated fields don’t belong in table!

  7. Queries • Usually we ask about info from 2+ tables. • By default, a query will perform an operation called a Cartesian Product, which gives all possible combinations. • Ex. Name and City tables:

  8. Cartesian Product • Given 2 sets, find all possible ordered pairs. • Analogously for more than 2 sets.  • Great example: choosing a menu. • Appetizer • Entrée • Dessert • Unfortunately, most DB queries are not like this! We get too many results.

  9. Relationships • We want to tell Access that there is a relationship between the tables, so we can create meaningful query. • One-to-many is most common • “Each city has one or more employees.” • Now, query will return 3 results instead of 6: Miami Bob Pittsburgh Mary Ken

  10. One-to-One • Can be useful if some information is confidential. • What if we didn’t have any relationship?

  11. 1-1 Query • When you combine tables that have a 1-1 relationship: Access will look for fields that are the same, and use this as a filter. • In previous example, we’ll have 2 results instead of 4.  Employee 101’s information Employee 102’s information • Let’s look at another example.

  12. What happens when we “join” these 1-1 tables?

  13. Relationship summary • When you have 2+ tables, there is almost always a relationship • They share one field in common. • Can you tell what it is? • Ex. Customers & Orders • Ex. Publishers & books • Ex. Students & Class roster

  14. Example

  15. Referential integrity Keep related records consistent Cascade delete: allow deletion of “one” Cascade update: allow update of “one” For example, changing someone’s CustomerID. One-many Relationships

  16. Many-to-many • Ex. Customers to products • Implement as 2 one-to-one • “Order details” table • Think of possible queries based on the 5 tables given in handout.

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