Difference between revisions of "Databases"
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* XML consists of tagged elements which can be nested, attributes of elements and the text (values/data) | * XML consists of tagged elements which can be nested, attributes of elements and the text (values/data) | ||
* XML document can be thought of as a tree with values/text forming the leaves. | * XML document can be thought of as a tree with values/text forming the leaves. | ||
| + | |||
| + | == Relational vs XML == | ||
| + | |||
| + | {| | ||
| + | ! | ||
| + | ! Relational | ||
| + | ! XML | ||
| + | |- | ||
| + | |Structure | ||
| + | |Tables | ||
| + | |Hierarchical/Tree | ||
| + | |- | ||
| + | |Schema | ||
| + | |Fixed in advance | ||
| + | |Flexible, self-describing. e.g. all elements need not have same attributes. (In relational, we would need to have NULL values). Inconsistencies in the structure is NOT a problem. | ||
| + | |- | ||
| + | |Queries | ||
| + | | Relatively simple | ||
| + | | Complicated compared to Relational / SQL. | ||
| + | |- | ||
| + | |Ordering | ||
| + | | Fundamentally UNORDERED. e.g. Order by clause is required in SQL in case order is desired. | ||
| + | | Ordering is implied - e.g. the way the text is laid out in the XML document. | ||
| + | |- | ||
| + | |Implementation | ||
| + | | | ||
| + | |15.00 | ||
| + | |} | ||
Revision as of 23:27, 7 December 2013
Relational Databases
- Set of named relations (tables)
- Each relation has a set of named attributes (columns)
- Each tuple (row) has a value for each attribute
- Each attribute has a type (or domain)
- All queries return relations (tables), so it can said to be compositional or closed.
XML Data
- Alternative to relational model to store data
- Standard for data representation and exchange
- Document format similar to HTML, however tags represent content instead of formatting.
- XML consists of tagged elements which can be nested, attributes of elements and the text (values/data)
- XML document can be thought of as a tree with values/text forming the leaves.
Relational vs XML
| Relational | XML | |
|---|---|---|
| Structure | Tables | Hierarchical/Tree |
| Schema | Fixed in advance | Flexible, self-describing. e.g. all elements need not have same attributes. (In relational, we would need to have NULL values). Inconsistencies in the structure is NOT a problem. |
| Queries | Relatively simple | Complicated compared to Relational / SQL. |
| Ordering | Fundamentally UNORDERED. e.g. Order by clause is required in SQL in case order is desired. | Ordering is implied - e.g. the way the text is laid out in the XML document. |
| Implementation | 15.00 |
