NoSQL Flashcards
Strengths of RDBMS (4)
- Consistency (ACID)
- Integration of data with schema normalization
- SQL language well known
- Robust (40+ years in organizations)
Weaknesses of RDBMS (4)
- Bad scaling
- Prioritizes consistency over latency
- Schema rigidity (no evolution)
No SQL common features (4)
- No just rows and tables
- Freedom from joins
- Schemaless or soft-schema
- Distributed architecture (cluster)
Can NoSQL systems be used for OLAP?
Possibly, but through analytical tools like Spark
4 main data models seen in NoSQL
- Key-value
- Document
- Wide column
- Graph
Graph data model
Focuses on relationship between data elements with vertices representing the entity, arcs representing relationship between entities, and properties descriping the vertices
2 examples of graph database queries
- Find friends of friends
(user)-[:KNOWS]-(friend)-[:KNOWS]-(foaf) - Find shortest path between A and B
shortestPath(:KNOWS*…5]-(userB))
What is the opposite of Graph Modeling?
Aggregate modeling
(key-value, document, wide-column)
What do we call tables in the document data model?
Collections, which hold a list of documents (often JSON format)
What does each document need to contain in the document data model? (2)
A set of fields corresponding to Key-value pair and mandatory ID
{
“_id”: 1,
“name”: “Martin”,
“adrs”: [
{“street”:”Adam”, “city”:”Chicago”, “state”:”illinois”, “code”:60007},
{“street”:”9th”, “city”:”NewYork”, “state”:”NewYork”, “code”:10001}
],
“orders”: [ {
“orderpayments”:[
{“card”:477, “billadrs”: {“street”:”Adam”, “city”:”Chicago”, “state”:”illinois”, “code”:60007}},
{“card”:457, “billadrs”: {“street”:”9th”, “city”:”NewYork”, “state”:”NewYork”, “code”:10001}}
],
“products”:[
{“id”:1, “name”:”Cola”, “price”:12.4},
{“id”:2, “name”:”Fanta”, “price”:14.4}
],
“shipAdrs”: {“street”:”9th”, “city”:”NewYork”, “state”:”NewYork”, “code”:10001}
}]
We can query this into different sections, such as Product Collection and Order Collection to return document with just those relevant fields
What does a key contain and what does a value contain in document data model
unique string (path, queries, REST calls, ID)
BLOB (binary large object) - HTML, pdf etc
Why is the value considered a black box when querying key-values in NoSQL?
There are no indexes on the values, no “where” clauses allowed. Schema information is often indicated in the key
Ex:
Key Value
user: 1234: name Enrico
Wide-column data model
in a RDBMS, data is stored in tables with rows that span a certain number of columns. If a particular record/row needs another column, you have to add it to the entire table. In Wide-column, you don’t
Key-value vs wide-column
Key-Value databases are the simplest model and can be thought of as a configuration file or a two-column table of keys with an associated value. Wide-column databases expand that key-value store concept across multiple columns, but only the columns that are needed for that record.
