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Typos fixes #7

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24 changes: 12 additions & 12 deletions Data Modeling.md
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Expand Up @@ -669,14 +669,14 @@ Examples of entities:
- Courses
- Examples of entity sets
- Professors and Students
- Data Science coruses: curriculms
- Data Science courses: curriculums

---
#### Syntax

![inline](./attachments/entities.png)

^ fields are what we call attribtues
^ fields are what we call attributes

### Relationships and Relationship Sets

Expand All @@ -690,7 +690,7 @@ Examples of entities:
- attendee
- enrollment

### Intution
### Intuition

![inline](./attachments/Relationship-syntax.png)

Expand All @@ -707,9 +707,9 @@ Examples of entities:

Each entity has a **value** for each of its attributes.

Also relationshis may have attributes called **descriptive attributes**.
Also relationships may have attributes called **descriptive attributes**.

### Intution
### Intuition

![inline 25%](./attachments/attrrel.png)

Expand Down Expand Up @@ -777,7 +777,7 @@ A professor advises many students but a student has only one advisor.

![inline](./attachments/many-to-many.png)

A course is associated to many insitute in the context of a curriculum
A course is associated to many institute in the context of a curriculum
An institute offers many courses within a curriculum

### Keys
Expand Down Expand Up @@ -895,7 +895,7 @@ Curriculum(<u>Institute\_ID</u>,<u>Course\_ID</u>)
### Normal Forms (Refresh)

- First Normal Form (1NF)
- A table has only atomic valued clumns.
- A table has only atomic valued columns.
- Values stored in a column should be of the same domain
- All the columns in a table should have unique names.
- And the order in which data is stored, does not matter.
Expand All @@ -912,7 +912,7 @@ Curriculum(<u>Institute\_ID</u>,<u>Course\_ID</u>)
### Modeling for Database: A note on Storage

- Storage is laid out in a row-oriented fashion
- For relational this is as close as the the tabular representation
- For relational this is as close as the tabular representation
- All the values from one row of a table are stored next to each other.
- This is true also for some NoSQL (we will see it again)
- Document databases stores documents a contiguous bit sequence
Expand Down Expand Up @@ -966,9 +966,9 @@ Four-Step Dimensional Design Process
[Mandatory Read](http://www.kimballgroup.com/wp-content/uploads/2013/08/2013.09-Kimball-Dimensional-Modeling-Techniques11.pdf)

^
- **Business processes** are crtical activities that your organization performs, e.g., registering students for a class.
- **Business processes** are critical activities that your organization performs, e.g., registering students for a class.
- The **grain** establishes exactly what a single fact table row represents. Three common grains categorize all fact tables: transactional, periodic snapshot, or accumulating snapshot.
- **Dimensions** provide contex to business process events, e.g., who, what, where, when, why, and how.
- **Dimensions** provide context to business process events, e.g., who, what, where, when, why, and how.
- :wq
- **Facts** are the measurements that result from a business process event and are almost always numeric.

Expand Down Expand Up @@ -1089,7 +1089,7 @@ A distributed file system stores files across a large collection of machines whi
### Name Node

- A single node that keeps the metadata of HDFS
- Keeps the metedata in memory for fast access
- Keeps the metadata in memory for fast access
- Periodically flushes to the disk (FsImage file) for durability
- Name node maintains a daemon process to handle the requests and to receive heartbeats from other data nodes

Expand Down Expand Up @@ -1136,7 +1136,7 @@ A distributed file system stores files across a large collection of machines whi

### HDFS High-availability

- Each NameNode is backedup with a slave other NameNode that keeps a copy of the catalog
- Each NameNode is backed up with a slave other NameNode that keeps a copy of the catalog

- The slave node provides a failover replacement of the primary NameNode

Expand Down