Appendix C: Syntax Conventions | Beginning XML Databases (Wrox Beginning Guides)

Syntax diagrams in this book use Backus-Naur Form syntax notation conventions. Backus-Naur Form has become the de facto standard for most computer texts :

Angle brackets: < ... >. Angle brackets are used to represent names of categories and are also known as substitution variable representation . In this example, <table> will be replaced with a table name :
```
   SELECT * FROM <table>;   
```
The preceding code becomes:
```
   SELECT * FROM country;   
```
OR: . A pipe or character represents an OR conjunction meaning either can be selected. In this case, all or some fields can be retrieved, some meaning one or more:
```
   SELECT { *  { <field>, ... } } FROM <table>;   
```
The preceding code becomes:
```
   SELECT name, id, population FROM country;   
```

Optional: [ ]. In a SELECT statement, a WHERE clause is syntactically optional:

   SELECT * FROM <table> [ WHERE <field> = ... ];

The preceding code becomes:

   SELECT * FROM name WHERE name='England';

At least one of: { }. For example, the SELECT statement must include one of *, or a list of one or more fields:
```
   SELECT { *  { <field>, ... } } FROM <table>;   
```
The preceding code becomes:
```
   SELECT name, id, population FROM country;   
```

This is not a precise interpretation of Backus-Naur Form where curly braces usually represent zero or more. In this book, curly braces represent one or more iterations, never zero.