The programmer can define methods for structures, which can be usedin queries with the same syntax as normal structure components. Such a method should have no arguments except a pointer to the object to whichit belongs (the <code>this</code> pointer in C++), and should returnan atomic value (of boolean, numeric, string or reference type).Also the method should not change the object instance (immutable method).If the method returns a string, this string should be allocated using the<code>new char</code> operator, because it will be deleted after copying of its value.<P>So user-defined methods can be used for the creation of <I>virtual</I> components - components which are not stored in the database, but instead are calculatedusing values of other components. For example, the FastDB <code>dbDateTime</code>type contains only integer timestamp components and such methodsas <code>dbDateTime::year()</code>, <code>dbDateTime::month()</code>...So it is possible to specify queries like: "<code>delivery.year = 1999</code>"in an application, where the <code>delivery</code> record field has <code>dbDateTime</code> type. Methods are executed in the context of theapplication, where they are defined, and are not available to other applications and interactive SQL.<P><H3><A NAME = "array">Arrays</A></H3>FastDB accepts arrays with dynamic length as components of records. Multidimensional arrays are not supported, but it is possible todefine an array of arrays. It is possible to sort records in the result setby length of array field.FastDB provides a set of special constructions for dealing with arrays:<P><OL><LI>It is possible to get the number of elements in the array by the <code>length()</code> function. <LI>Array elements can be fetched by the<code>[]</code> operator.If an index expression is out of array range, an exception will be raised.<LI>The operator <code>in</code> can be used to check if an array containsa value specified by the left operand. This operation can be used only for arrays ofatomic type: with boolean, numeric, reference or string components.<LI>Array can be updated using <code>update</code> method which creates copy of the array and returnsnon-constant reference.<LI>Iteration through array elements is performed by the <code>exists</code> operator. A variable specified after the <code>exists</code> keyword can be usedas an index in arrays in the expression preceeded by the <code>exists</code>quantor. This index variable will iterate through all possible arrayindex values, until the value of the expression will become <code>true</code> orthe index runs out of range. The condition<PRE>        exists i: (contract[i].company.location = 'US')</PRE>will select all details which are shipped by companies located in 'US', while the query<PRE>        not exists i: (contract[i].company.location = 'US')</PRE>will select all details which are shipped from companies outside 'US'.<P>Nested <code>exists</code> clauses are allowed. Using nested <code>exists</code>quantors is equivalent to nested loops using the correspondentindex variables. For example the query<PRE>        exists column: (exists row: (matrix[column][row] = 0))</PRE>will select all records, containing 0 in elements of a <code>matrix</code> field, which has type array of array of integer.This construction is equivalent to the followingtwo nested loops:<PRE>       bool result = false;       for (int column = 0; column < matrix.length(); column++) {             for (int row = 0; row < matrix[column].length(); row++) { 	         if (matrix[column][row] == 0) {                      result = true;		     break;                 }            }       }</PRE>The order of using indices is essential! The result of the following query execution<PRE>        <code>exists row: (exists column: (matrix[column][row] = 0))</code></PRE>will be completely different from the result of the previous query.In the last case, the program simply hangs due to an infinite loopin case of empty matrices. </OL><H3><A NAME = "string">Strings</A></H3>All strings in FastDB have varying length and the programmer should notworry about specification of maximal length for character fields. All operations acceptable for arrays are also applicable to strings. In addition to them, strings have a set of own operations.First of all, strings can be compared with each other using standardrelation operators. At present, FastDB supports only theASCII character set (corresponds to type <code>char</code> in C) andbyte-by-byte comparison of strings ignoring locality settings.<P>The operator <code>like</code> can be used for matching a string with a pattern containing special wildcard characters'%' and '_'. The character '_' matches any single character, while the character '%' matches zero or more characters.An extended form of the <code>like</code> operator together withthe <code>escape</code> keyword can be used to handle thecharacters '%' and '_' in the pattern as normal characters if they are preceded by a special escape character, specified afterthe <code>escape</code> keyword.<P> It is possible to search substrings within a string by the <code>in</code>operator. The expression <code>('blue' in color)</code> will be truefor all records which <code>color</code> field contains 'blue'. If the length of the searched string is greater than some threshold value (currently 512), a Boyer-Moore substring search algorithm is used instead of a straightforward search implementation.<P>Strings can be concatenated by <code>+</code> or <code>||</code> operators.The last one was added for compatibility with the ANSI SQL standard.As far as FastDB doesn't support the implicit conversion to string type in expressions, the semantic of the operator <code>+</code> can be redefined forstrings.<P><H3><A NAME = "reference">References</A></H3>References can be dereferenced using the same dot notation as used foraccessing structure components. For example the following query<PRE>        company.address.city = 'Chicago'</PRE>will access records referenced by the <code>company</code> component ofa <code>Contract</code> record and extract the city component of the<code>address</code> field of the referenced record from the <code>Supplier</code> table.<P>References can be checked for <code>null</code> by <code>is null</code>or <code>is not null</code> predicates. Also references can be compared for equality with each other as well as with the special <code>null</code>keyword. When a null reference is dereferenced, an exception is raisedby FastDB.<P>There is a special keyword <code>current</code>, whichduring a table search can be used to refer to the current record.Usually , the <code>current</code>keyword is used for comparison of the current record identifier withother references or locating it within an array of references. For example, the following query will search in the <code>Contract</code> table for all active contracts(assuming that the field <code>canceledContracts</code> has a<code>dbArray&lt; dbReference&lt;Contract&gt; &gt;</code> type): <PRE>        current not in supplier.canceledContracts</PRE><P>FastDB provides special operators for recursive traverse of records by references:<PRE>     <code>start from</code> <I>root-references</I>     ( <code>follow by</code> <I>list-of-reference-fields</I> )</PRE>The first part of this construction is used to specify root objects. The nonterminal <I>root-references</I> should be a variable of reference orof array of reference type. The two special keywords <code>first</code> and<code>last</code> can be used here, locating the first/last record in the tablecorrespondingly. If you want to check all recordsreferenced by an array of references or a single reference field for some condition, then thisconstruction can be used without the <code>follow by</code> part.<P>If you specify the follow by part, then FastDB will recursively traverse the table of records, starting from the rootreferences and using a <I>list-of-reference-fields</I> for transition between records.The <I>list-of-reference-fields</I> should consist of fields ofreference or of array of reference type. The traverse is done in depth firsttop-left-right order (first we visit the parent node and then the siblings in left-to-right order).The recursion terminates when a null reference is accessedor an already visited record is referenced. For example the followingquery will search a tree of  records with weight larger than 1 in TLR order:<P><PRE>        "weight > 1 start from first follow by left, right"</PRE><P>For the following tree:<PRE>                              A:1.1              B:2.0                             C:1.5      D:1.3         E:1.8                F:1.2         G:0.8</PRE>the result of the query execution will be: <PRE>('A', 1.1), ('B', 2.0), ('D', 1.3), ('E', 1.8), ('C', 1.5), ('F', 1.2)</PRE><P>As was already mentioned FastDB always manipulates with objects and doesn't accept joins. Joins can be implemented using references. Consider the classical <code>Supplier-Shipment-Detail</code> examples: <PRE>struct Detail {     char const* name;    double      weight;        TYPE_DESCRIPTOR((KEY(name, INDEXED), FIELD(weight)));};struct Supplier {     char const* company;    char const* address;    TYPE_DESCRIPTOR((KEY(company, INDEXED), FIELD(address)));};struct Shipment {     dbReference&lt;Detail&gt;   detail;    dbReference&lt;Supplier&gt; supplier;    int4                  price;    int4                  quantity;    dbDateTime            delivery;    TYPE_DESCRIPTOR((KEY(detail, HASHED), KEY(supplier, HASHED), 		     FIELD(price), FIELD(quantity), FIELD(delivery)));};</PRE>We want to get information about delivery of some concrete details from some concretesuppliers. In relational database this query will be written something like this:<PRE>     select from Supplier,Shipment,Detail where                  Supplier.SID = Shipment.SID and Shipment.DID = Detail.DID 		 and Supplier.company like ? and Supplier.address like ?		 and Detail.name like ? </PRE>In FastDB this request should be written as: <PRE>     dbQuery q = "detail.name like",name,"and supplier.company like",company,	         "and supplier.address like",address,"order by price";</PRE>     FastDB will first perform index search in the table <code>Detail</code> for detailsmatching the search condition. Then it performs another index search to locate shipment records referencing selected details. Then sequential search is used to check the rest ofselect predicate.<P><H3><A NAME = "function">Functions</A></H3><TABLE BORDER ALIGN="center"><CAPTION>Predefined functions</CAPTION><TR><TH>Name</TH><TH>Argument type</TH><TH>Return type</TH><TH>Description</TH></TR><TR><TD>abs</TD><TD>integer</TD><TD>integer</TD><TD>absolute value of the argument</TD</TR><TR><TD>abs</TD><TD>real</TD><TD>real</TD><TD>absolute value of the argument</TD</TR><TR><TD>integer</TD><TD>real</TD><TD>integer</TD><TD>conversion of real to integer</TD</TR><TR><TD>length</TD><TD>array</TD><TD>integer</TD><TD>number of elements in array</TD</TR>