Many to Many

Everything allowed

• Many to one

• Only one end at arrow side

• None is okay

• One to one

• None is okay

Exaclt one,

none is not an option

CREATE TABLE [Name] (

[row name] [data type] <Constraint>,

[another row name] [data type] <Constraint>,

<PRIMARY KEY (some row name, some other row name)>

);

• NOT NULL

• DEFAULT value

• UNIQUE

• PRIMARY KEY

  • unique

  • not null

• CHECK([some bool /a subquerry])

• REFERENCES [Table name]([attribute name])

• INT

• CHAR([x])

  • Lenght must match x

• VARCHAR([x])

  • Lenght < x

• DATE

• TIME

• Conflict if the following on same element

  • R/W

  • W/R

  • W/W

• Not if

  • R/R

• Edges on conflicting transactions

  • Arrow from first to later statement

• Sequelizable if graph acyclic

Undo/Redo

• Log can be temporarilly in mem, but as to be on stable disk before tansaction can be comitted to mem

• Operation

  • Log every edit (to cache)

  • output to disk some time later

• Recovery

  • Undo all T without commit

  • Redo all comitted T

• + fast during operation

• + allows have done transactions on disk

• - complex recovery

No Undo/Redo

• Stable log required

• Operation

  • log everything

  • ouput to disk later, but only after log is on stable storage

• Recovery

  • Redo comitted T

  • No half messages as only comitted edits are on stable storage

• + Faster recovery

• + smaller log, no before values needed

• - limits operations to mem

  
  

  Undo/ No Redo

  • Stable log required

  • Operation

    • log everything

    • ouput to disk immediatly, together with commit to stable

  • Recovery

    • Undo all half done T (not comitted)

    • All commited have to be on disk anyways

  • + Faster recovery

  • + smaller log, no after values needed

  • - many many disk IO

  
  

Cheap (do first)

1. Restrictive Selection a like “Peter”

2. Other selection

3. Projection

4. Joint

Very expencive, do last

• Keine Abhängigkeit der Attribute untereinander

•