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UML 2 State Machine diagrams are derived from UML 1.4 Statecharts, which in turn were derived from Harel Statecharts.1 State Machine diagrams are a way to model systems that work in modes or states. In each state, the system responds to events in a certain way. Events, called triggers in the context of UML 2 State Machine diagrams, can be generated externally or internally, with respect to the system. Triggers produce transitions between states. You model a system by showing its states as boxes and its state transitions as arrows. Figure 6-1 shows a simple State Machine diagram for an elevator in a two-story building.

The DBA_FREE_SPACE view tells you how much free space you have in the database at any given moment. You can use the query in Listing 6-5 to find out how much free space you have in your

tablespaces. Note that space belonging to a table that you dropped and is in the Recycle Bin shows up as free space in this view. However, you can t use it for any other object. You get the space back only after you permanently remove the item with the ALTER TABLE . . . PURGE statement. Listing 6-5. Querying the DBA_FREE_SPACE View SQL> SELECT tablespace_name, SUM(bytes) 2 FROM DBA_FREE_SPACE 3* GROUP BY tablespace_name; TABLESPACE_NAME --------------CWMLITE DRSYS EXAMPLE INDX ODM SYSTEM TOOLS UNDOTBS1 USERS XDB 10 rows selected. SQL> SUM(BYTES) ---------11141120 10813440 262144 26148864 11206656 4325376 4128768 202047488 26148864 196608

As you re aware, the Oracle database contains several kinds of segments: table, index, undo, and so on. The DBA_SEGMENTS data dictionary view shows the segment name and type and the tablespace the segment belongs to, among other things. The view provides you with detailed information on the various segments in the database, as seen in the example in Listing 6-6. Listing 6-6. Querying the DBA_SEGMENTS View SQL> 2 3 4 5 6 7 8 9* SELECT tablespace_name, segment_name, segment_type, extents, /*Number of extents in the segment*/ blocks, /*Number of db blocks in the segment*/ bytes /*Number of bytes in the segment*/ FROM dba_segments WHERE owner = 'HR'; SEGMENT_NAME -----------REGIONS LOCATIONS DEPARTMENTS JOBS EMPLOYEES JOB_HISTORY REG_ID_PK COUNTRY_PK SEGMENT_TYPE EXTENTS BLOCKS BYTES ------------ ------- ------ -----TABLE 1 8 65,536 TABLE 1 8 65,536 TABLE 1 8 65,536 TABLE 1 8 65,536 TABLE 1 8 65,536 TABLE 1 8 65,536 INDEX 1 8 65,536 INDEX 1 8 65,536

1. David Harel, Statecharts: A Visual Formalism for Complex Systems, Science of Computer Programming, June 1987.

1 1 1

8 8 8

65,536 65,536 65,536

Figure 6-1. A UML State Machine diagram showing states and transitions You label transitions to show their causes, which are called triggers. You can qualify triggers with a guard condition specifying the conditions that must apply in order for the trigger to be recognized. You show guard conditions on diagrams by adding the condition in square brackets after the trigger name. Figure 6-2 shows an example.

The DBA_DATA_FILES data dictionary view is yet another extremely useful view that you ll refer to often while managing the space in your database. You can query the view to find out the names of all the datafiles, the tablespaces they belong to, and datafile information such as the number of bytes and blocks and the relative file number. A simple query on the DBA_DATA_FILES view shows all your datafiles, as shown in Listing 6-7. Listing 6-7. Querying the DBA_DATA_FILES View SQL> SELECT file_name, tablespace_name FROM DBA_DATA_FILES; FILE_NAME -----------------------------------------C:\ORACLENT\ORADATA\MANAGER\SYSTEM01.DBF C:\ORACLENT\ORADATA\MANAGER\UNDOTBS01.DBF C:\ORACLENT\ORADATA\MANAGER\CWMLITE01.DBF C:\ORACLENT\ORADATA\MANAGER\DRSYS01.DBF C:\ORACLENT\ORADATA\MANAGER\EXAMPLE01.DBF C:\ORACLENT\ORADATA\MANAGER\INDX01.DBF C:\ORACLENT\ORADATA\MANAGER\TOOLS01.DBF C:\ORACLENT\ORADATA\MANAGER\USERS01.DBF 8 rows selected. SQL> TABLESPACE_NAME ------------SYSTEM UNDOTBS CWMLITE DRSYS EXAMPLE INDX TOOLS USERS

The DBA_DATA_FILES view is especially useful when you join it with another data dictionary view, as the example in Listing 6-8 illustrates. The query produces a report showing you the tablespace sizes, free and used space, and the percentage of used space in each tablespace. At the end, you also get the sum of total space allocated to all the tablespaces, and the breakdown of free and used space in the database. Listing 6-8. Joining Multiple Data Dictionary Views BREAK ON REPORT COMPUTE SUM OF tbsp_size ON REPORT compute SUM OF used ON REPORT compute SUM OF free ON REPORT COL COL COL COL COL SQL> 2 3 4 tbspname tbsp_size used free pct_used FORMAT FORMAT FORMAT FORMAT FORMAT a20 999,999 999,999 999,999 999 HEADING 'Tablespace Name' HEADING 'Size|(MB)' HEADING 'Used|(MB)' HEADING 'Free|(MB)' HEADING'% Used' tbspname tbsp_size, used, free,

public string LookupAddress(string theRecipientName) { if (recipients.ContainsKey(theRecipientName)) return recipients[theRecipientName] as string;

SELECT df.tablespace_name sum(df.bytes)/1024/1024 nvl(sum(e.used_bytes)/1024/1024,0) nvl(sum(f.free_bytes)/1024/1024,0)