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Why PL/SQL?

Pure SQL may have poor performance. With embedded SQL, each statement is individually sent over the network to be executed on the server. PL/SQL blocks can be sent over.




PL/SQL procedures and functions are stored in a parsed and compiled form on the DB server so parsing overhead and network traffic are reduced.



What additional functionality is there with PL/SQL?

Loops, arrays/collections, functions, variables, exception handling, code blocks.

What does it mean when DBMSs are 'value-based'?

Relationships between and attributes of real-life entities are represented by storage of values in table rows.

What is an object DBMS? (3)

- Supports complex object structures e.g. collections


- Encapsulates objects by providing procedures to indirectly access and manipulate the internal data representation


- Support classes and inheritance

What is a key-value store?

Storage of values in the form of bytes, retrieval by keys.

What is a document store?

Like key-value but the values are actual documents with a structure that may be referenced by the API.




MongoDB

What is a graph store?

Information is represented by nodes and edges with properties.

What are the advantages of NoSQL databases?

- Scalability and extensibility (across servers rather than all on one server that needs to be big enough)


- Flexibility

What are the disadvantages of NoSQL databases?

- Lack of extensive concurrency control and recovery capabilities


- Lack of ACID compliance

What is a column store?

Columns are stored conceptually as a vector of elements consisting of an ID for a row with the encoded values.

Advantages of a column store?

Enables compression, efficient parallel execution using pipelining techniques.

Advantages of a document store?

Flexibility, as there are no fixed schemas.


For example in MongoDB all documents are in a JSON-ish format - fields can be added or deleted, and can be different across the collection.