Abstract:
A method for extracting metadata for plural related objects of different types from a database includes defining a heterogeneous object type as a collection of database objects of different types. Upon a request to fetch a particular heterogeneous object, member objects of the heterogeneous object are fetched from the particular heterogeneous object in a specific order based on the definition of the heterogeneous object&#39;s type, such as a valid order for re-creating the particular heterogeneous object. The set of member objects to be fetched can be restricted according to at least one specified filter, which itself may be translated into a second filter according to a type of a member object being fetched. Such translated filters can inherit values from the filter specified in the request for the particular heterogeneous object type, or can have a fixed value of some data type. The extracted metadata can be formatted to recreate the particular heterogeneous object.

Description:
BACKGROUND 
   The logical structure of a typical relational database is determined by its dictionary objects. These objects can be of a number of object types, e.g., tablespaces, users, tables, views, sequences, stored procedures, etc. 
   The Oracle Metadata API, introduced in Oracle 9i, provides a central facility for extracting metadata for one or more objects of a specific object type. The 9i implementation uses an OPEN-FETCH-CLOSE programming model: the user issues an OPEN for a particular object type and then repeatedly FETCHes objects of that type; upon completion, the user CLOSEs the object type context. A user can specify one or more filters that restrict the set of objects to be fetched. The Oracle 9i implementation provides a powerful and flexible mechanism for fetching objects within a particular object type. 
   This API is described in U.S. application Ser. No. 09/672,914, filed on Sep. 28, 2000, “Aggregating and manipulating dictionary metadata in a database system,” the entire teachings of which are incorporated by reference herein in their entirety. 
   SUMMARY 
   Often, a user may wish to extract the metadata for a logical set of objects that belong to different object types while comprising a logical unit. Examples are (1) a table and all of its dependent objects (constraints, indexes, grants, etc.); (2) all objects in a schema (tables, views, types, procedures, etc.); (3) all objects in the database (tablespaces, users, rollback segments, etc., as well as schemas and their contents). 
   Furthermore, the user may wish to take this extracted metadata and use it to recreate the logical set of objects on another database. To recreate the set of objects, however, they must be created in a specific order, e.g., a table before its indexes. Unfortunately, the creation order is frequently not obvious. 
   In prior solutions, users had to write custom code encapsulating knowledge of the objects making up the logical set, as well as the creation order for the objects. The Oracle Export utility is one such custom program. Such custom programs are usually well-designed for their specific purpose but can be difficult to adapt to new uses. 
   The present system can enhance the Oracle Metadata API described in U.S. Ser. No. 09/672,914 with “heterogeneous object types,” i.e., collections of objects that, although of different object types, nevertheless comprise a logical unit. The programming model can be the same OPEN-FETCH-CLOSE model used in Oracle 9i. The differences are that (1) the user specifies, in the OPEN statement, the name of a heterogeneous object type, (2) the objects fetched belong to different homogeneous object types, and (3) the objects are returned in a valid creation order. 
   A particular embodiment of the present system is a method for extracting metadata for plural related objects of different types from a database. The method can include defining a heterogeneous object type as a collection of database objects of different types. Upon a request to fetch a particular heterogeneous object, member objects of the heterogeneous object can be fetched from the particular heterogeneous object. Member objects can be returned in a specific order, such as a valid order for recreating the particular heterogeneous object, based on the definition of the heterogeneous object&#39;s type. 
   Exemplary heterogeneous object types are table export, database export, schema export and tablespace export types. Member objects can be homogeneous object types, or can be other heterogeneous object types. 
   The set of member objects to be fetched can be restricted according to at least one specified filter, which itself may be translated into a second filter according to a type of a member object being fetched. 
   In a particular embodiment, a first table can specify whether an object type is a heterogeneous or a homogeneous object type. A second table can then define the specific order in which member types for a given heterogeneous object type are to be returned. Upon a fetch command, member objects can be fetched according to the specific order defined in the second table. A third table can specify filters that can be applied to a particular heterogeneous object type, and a fourth table can specify filter translations for individual member object types. Such translated filters can inherit values from the filter specified in the request for the particular heterogeneous object type. Alternatively, a filter can have a fixed value of some data type, such as text, boolean, numeric, date, etc. 
   More particularly, the extracted metadata can be formatted using a markup language, such as XML. This markup language-formatted data can be translated into statements formatted to recreate the particular heterogeneous object. 
   In the present system, object metadata can be extracted from a relational database using just a single request for metadata for a logical unit within the database, where the logical unit comprises plural objects of different types. The requested metadata can then be extracted, and returned in an order in which the logical unit can be recreated on this or another database. While the single request may contain multiple fetches, it is a single request in that only one object type (i.e., the particular heterogeneous object type) is opened and the user does not need to be aware of the internal dependencies to extract all of the member objects. 
   A logical unit may comprise, for example, a table and its dependent objects, such as, but not limited to, constraints, indexes and/or grants. Other logical units may comprise, but are not limited to, schemas and databases. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the database system having heterogeneous object types will be apparent from the following more particular description of particular embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. 
       FIG. 1  is a schema diagram illustrating the objects created in an example of the present system and their relationships. 
       FIG. 2  is a schematic diagram illustrating a metaview$ table which, in addition to supporting homogeneous object types, supports heterogeneous object types of the present system. 
       FIG. 3  is a schematic diagram illustrating a metafilter$ table which, in addition to supporting homogeneous object types, supports heterogeneous object types of the present system. 
       FIG. 4  is a schematic diagram illustrating a metascript$ table, which is used to support heterogeneous object types of the present system. 
       FIG. 5  is a schematic diagram illustrating a metascriptfilter$ table, which is used to support heterogeneous object types of the present system. 
       FIG. 6  is a block diagram of representative organization of an embodiment of the present system. 
   

   DETAILED DESCRIPTION 
   The present system adds heterogeneous types to the Metadata API previously described by U.S. application Ser. No. 09/672,914. 
   Particular heterogeneous object types are added by inserting rows into dictionary, or system, tables. One table (metaview$) contains the names of all object types, with a flag indicating whether the type is homogeneous or heterogeneous. Another table (metascript$) defines the member types belonging to the heterogeneous type and their order. The code implementing the FETCH function determines whether the object type is homogeneous, in which case it does the normal processing, or whether the object type is heterogeneous, in which case it calls itself recursively for each of the member types. 
   Heterogeneous object types can be recursively nested, i.e., one heterogeneous type can be a member of another heterogeneous type. As with homogeneous object types, users can specify filters on a heterogeneous object type that restrict the set of objects to be fetched. These filters are translated into filters on the member types; the translation is specified in another dictionary table (metascriptfilter$). 
   EXAMPLE 
   The following example demonstrates how the metadata API (dbms_metadata) fetches a heterogeneous object—that is, an ordered set of objects which, although they are of different object types, nevertheless comprise a logical unit. In this example, the heterogeneous object is of type TABLE_EXPORT, consisting of a table and its indexes. 
   First, assume the following script is executed to create, in schema “SCOTT,” a table named “EMPLOYEE” having two columns, “empno” and “empname.” Two indexes are created on the table, namely “EMP_IND 1 ” and “EMP_IND 2 .” Connection to the schema is presumed.
     create table EMPLOYEE (
       empno number,   empname varchar 2 (30));   
       create index EMP_IND 1  on EMPLOYEE(empno);   create index EMP_IND 2  on EMPLOYEE(empname);   

     FIG. 1  is a schema diagram illustrating the resulting objects and their relationships. A heterogeneous object  20  of type TABLE_EXPORT comprises the table “EMPLOYEE”  12 , having the two columns empno  18  and empname  19 , and the two indexes  14 ,  16  on each of the columns. 
   We now fetch, using a single request comprising a single OPEN, one or more FETCHES, and a single CLOSE command, the heterogeneous TABLE_EXPORT object  20  that comprises the table  12  and its two indexes  14 , 16 . The members  12 , 14 ,  16  of the heterogeneous object  20  are returned in a valid creation order. That is, the table  12  is returned first, since it must be created before the indexes  14 , 16 . Below is an exemplary script using the present invention to extract a heterogeneous object. Put_clob( ) represents some simple function which can print out the contents of a clob (a character large object).
     declare
       h NUMBER;   th NUMBER;   c clob;   
       begin
       h:=dbms_metadata.open(‘TABLE_EXPORT’);   dbms_metadata.set_filter(h,‘NAME’,‘EMPLOYEE’);   dbms_metadata.set_filter(h, ‘SCHEMA’,‘SCOTT’)   th:=dbms_metadata.add_transform(h,‘DDL’);   LOOP
           dbms_lob.createtemporary(c,true);   dbms_metadata.fetch_clob(h,c);   EXIT WHEN c IS NULL;   put_clob(c);   dbms_lob.freetemporary(c);   
           END LOOP;   dbms_metadata.close(h);   
       END;   

   Each of the dbms_metadata calls is described in U.S. application Ser. No. 09/672,914. As disclosed in that application, calls apply only to homogeneous objects. The present system expands the dbms_metadata interface to include heterogeneous object types such as DATABASE_EXPORT, SCHEMA_EXPORT, TABLE_EXPORT and TABLESPACE_EXPORT. 
   The OPEN call, dbms_metadata.open( ), provides the heterogeneous class, in this case TABLE_EXPORT, for which metadata is being requested. A handle h is returned to be used in all subsequent operations of the set of objects for which metadata is being requested. 
   The first FILTER call, dbms_metadata.set_filter( ), restricts the search to the table named “EMPLOYEE,” while the second FILTER call restricts the search to the schema named “SCOTT.” 
   The call to dbms_metadata.add_transform( ) causes the output of the FETCH command (see below), which is normally formatted in XML, to be transformed to DDL. The result is then directly usable for recreating the heterogeneous object  20  on another database. 
   Within the loop, bracketed by the LOOP and END LOOP lines, a temporary character large object (clob) is created. The FETCH call, dbms_metadata.fetch_clob( ), returns an member object from the designated heterogeneous object as a clob. If all such objects have already been returned, a NULL is returned and the loop is exited. 
   Otherwise, for purposes of this example, the object is displayed (put_clob( )). Next, the temporary clob is freed up. The loop repeats, each time returning a different member object, until all members have been fetched. 
   Finally, the CLOSE call, dbms_metadata.close( ) is made to end the request. 
   Execution of the above script results in the following output, where SCOTT is the name of the schema to which the table and the indexes belong.
      . . .   CREATE TABLE “SCOTT”.“EMPLOYEE”   (“EMPNO” NUMBER,
       “EMPNAME” VARCHAR2(30)   
       ) PCTFREE  10  PCTUSED  40  INITRANS  1  MAXTRANS  255  LOGGING STORAGE(INITIAL  10240  NEXT  10240  MINEXTENTS  1  MAXEXTENTS  121  PCTINCREASE  50  FREELISTS  1  FREELIST GROUPS  1  BUFFER_POOL DEFAULT)   TABLESPACE “SYSTEM”   . . .   . . .   CREATE INDEX “SCOTT”.“EMP_IND 1 ” ON “SCOTT”.“EMPLOYEE” (“EMPNO”) PCTFREE  10  INITRANS  2  MAXTRANS  255  STORAGE(INITIAL  10240  NEXT  10240  MINEXTENTS  1  MAXEXTENTS  121  PCTINCREASE  50  FREELISTS  1  FREELIST GROUPS  1  BUFFER_POOL DEFAULT)   TABLESPACE “SYSTEM”   . . .   . . .   CREATE INDEX “SCOTT”.“EMP_IND 2 ” ON “SCOTT”.“EMPLOYEE”   (“EMPNAME”)   PCTFREE  10  INITRANS  2  MAXTRANS  255  STORAGE(IMTIAL  10240  NEXT  10240  MINEXTENTS  1  MAXEXTENTS  121  PCTINCREASE  50  FREELISTS  1  FREELIST GROUPS  1  BUFFER_POOL DEFAULT)   TABLESPACE “SYSTEM”   . . .   

   The result comprises three CREATE statements, one for the table, and one for each of the indexes. 
     FIGS. 2–5  are schematic diagrams of tables used to support heterogeneous object types. The tables of  FIGS. 2 and 3  have been defined in the prior art, but are used further to support heterogeneous objects types. The tables of  FIGS. 4 and 5  are new. 
     FIG. 2  illustrates four entries  31 – 34  in the metaview$ table  30 , which is described in U.S. application Ser. No. 09/672,914. This table contains the names of all object types. In an embodiment of the present invention, a new value, e.g., 2, in the properties field  43  is defined to indicate that the row identifies a heterogeneous object type. Here, the presence of the value 2 in the properties field  43  of each of rows  31 – 34  indicates that the types identified in the type field  41 , i.e., DATABASE_EXPORT. SCHEMA_EXPORT, TABLESSPACE_EXPORT and TABLE_EXPORT respectively, are heterogeneous object types. 
   The other fields  42 ,  44 – 49 , described in U.S. application Ser. No. 09/672,914, are not of any particular interest with respect to the present system, and are not discussed further. 
     FIG. 3  illustrates a metafilter$ table  50  used to implement an embodiment of the present system. This table is also described in U.S. application Ser. No. 09/672,914. In order to limit fetches to a particular logical unit, a filter is specified. The metafilter$ table  50  defines the set of filters that are valid for each object type. The filter field  53  provides the name of a filter, while the type field  54  holds the name of a type for which the named filter is valid. For example, here rows  51  and  52  indicate respectively that “NAME” and “SCHEMA” are valid filters that can be applied to heterogeneous type TABLE_EXPORT. 
     FIG. 4  illustrates the metascript$ table  60 , a new table used to implement an embodiment of the present system. The metascript$ table  60  describes the member types of a given heterogeneous object type, as well as the order in which the different member types are to be fetched. 
   For each heterogeneous type, there is one row for each member type. The ptype field  64  holds the name of the heterogeneous type to which a particular row corresponds. The seq# field  65  is a sequence number. The 1type field  66  holds the leaf or member object name. Leaf or member objects are opened and fetched in the sequence indicated by the seq# field  65 . 
   The model field  67  identifies model properties. This field  67  is not particularly relevant to the present system in particular and is not discussed further. 
   Several rows  61 – 63  are illustrated for exemplary purposes. The corresponding sequence numbers in the seq# field  65  of each row indicate that, for a heterogeneous object of type TABLE_EXPORT, objects of type TABLE will be fetched first (row  61 , seq#=10), followed by OBJECT_GRANT objects (row  62 , seq#=20) and finally, in this example, by all INDEX objects (row  63 , seq#=30). Of course, in a live database, the rows can be in a random sequence, which is why a sequence number field  65  is needed. 
     FIG. 5  illustrates the metascriptfilter$ table  70 , which is also a new table created to implement an embodiment of the present system. The metascriptfilter$ table  70  translates the filter provided in the FILTER statement, and matched in field  53  from the metafilter$ table  50 , to a filter name for each member object type. 
   Each row in the metascriptfilter$ table  70  translates the filter name provided by the user to a type-specific filter. For example, a NAME filter can be specified for heterogeneous object type TABLE_EXPORT through a call such as the line in the above program:
         dbms_metadata.set_filter(h, ‘NAME’, ‘EMPLOYEE’)
 
where the heterogeneous object type&#39;s NAME filter is set to EMPLOYEE, such that only objects where NAME=EMPLOYEE are selected.
       

   The exemplary metacriptfilter$ table  70  of  FIG. 5  translates the NAME and SCHEMA filters for the TABLE_EXPORT object to NAME and SCHEMA filters for TABLE object, corresponding to rows  71  and  72  respectively, where seq#=10. Similarly, rows  73  and  74  translate the NAME and SCHEMA filters to BASE_OBJECT_NAME and BASE_OBJECT_SCHEMA for OBJECT_GRANT objects (seq#=20), and row  75  and  76  (seq#=30) translate the NAME and SCHEMA filters to BASE_OBJECT_NAME and BASE_OBJECT_SCHEMA for INDEX objects. 
   In the example provided, all of the member objects have filters whose values correspond to the NAME and SCHEMA filters on the TABLE_EXPORT object. However, a fixed text or boolean (e.g., TRUE or FALSE) value could be specified for a filter. 
   For predetermined or fixed value filters, the filter values are stored in the vcval field  84  for text values or in the bval  85  field for boolean values. If, on the other hand, the value is inherited from a filter passed to the script, then the name of the filter is stored in the pfilter field  83 . 
   The metascriptfilter$ table  70  can easily be extended to support fixed value filters of additional data types, such as numbers, dates, etc., by adding additional fileds. 
   The seq# field  81  of a row contains the sequence number and corresponds to the seq# field  65  of the metascript$ table ( FIG. 4 ). The filter field  82  contains the filter name if the value is not fixed. The pfilter field  83  contains the parent filter name. Finally, the model field  86  is not particularly relevant to the present system and is not discussed further. 
   In one embodiment of the present system, recursive OPEN calls are made specifying object types in order according to the metascript$ table. After each OPEN call, the metascriptfilter$ table is checked, and a SET_FILTER is executed with the appropriate filter name and value. 
   Thus, in the illustrative example, first TABLE objects where NAME=EMPLOYEE are fetched, followed by OBJECT_GRANTS objects where BASE_OBJECT_NAME=EMPLOYEE, then INDEX objects where BASE_OBJECT_NAME=EMPLOYEE, and so on. 
   The API allows a user to specify a filter for a specific member type. For example, when fetching objects from a DATABASE_EXPORT heterogeneous type, the user might want to filter out the SYSTEM tablespace (every database automatically has a SYSTEM tablespace, so it does not need to be recreated on a target database). To do this, the user may specify a NAME_EXPR filter that applies only to TABLESPACE objects, meaning “include any tablespace whose name is not ‘SYSTEM’”, e.g.,
         h:=dbms_metadata.open(‘DATABASE_EXPORT’);   dbms_metadata.set_filter(h,‘NAME_EXPR’,‘!=“SYSTEM’”,‘TABLESPACE’);       

     FIG. 6  is a block diagram of representative organization of an embodiment of the present system, although it would be understood by one skilled in the art that other organizations are possible which would still fall within the scope of the present invention. 
   Here, the metadata application program interface (API)  100  accepts heterogeneous object type requests  102  from a user or application. Such requests include, but are not limited to, OPEN and CLOSE commands as well as one or more SET_FILTER and FETCH commands. The commands are passed to a metadata extractor  104  which organizes fetches of the requested heterogeneous object type&#39;s member object types in the order dictated according to the metaview$ table  30  and the metascript$ table  60 . 
   A filter translator  106  translates heterogeneous object type filters named in the request  102  into a member object filter for each object type according to the metafilter$ table  50  and metascriptfilter$ table  70  as described previously. 
   The metadata extractor  104  then extracts, i.e., fetches, the member objects from one or more logical units  20 , i.e., according to the heterogeneous object type and the filters provided by the user/application in the request  102 . 
   In one embodiment of the present system, the metadata is extracted as an XML document. A formatter, or format translator,  108  formats the XML document into other formats such as DDL, according to the request  102 . 
   Finally, the API  100  returns this formatted data  110  to the user/application. 
   The present system gives the user a high-level interface for extracting the objects in a heterogeneous collection. The user does not need to know which objects belong to the collection or their creation order. 
   The filtering capabilities allow the user great flexibility in customizing the set of objects retrieved. 
   Because the definition of a heterogeneous type consists of rows in dictionary tables, it is easy to define and maintain new heterogeneous object types. In a custom program such as Oracle&#39;s Export utility, for example, adding a new heterogeneous object type requires extensive programming. 
   The present system represents an advance on the current Export utility, which fetches metadata for heterogeneous collections, but then writes the metadata opaquely to a file in a proprietary format. In contrast, the present system can make the metadata transparently available to any database user. 
   There is increasing demand for specialized heterogeneous collections, e.g., transportable tablespaces and application-specific subsets of objects. The present system can make new heterogeneous collections easy to define and maintain. 
   Those of ordinary skill in the art should recognize that methods involved in a DATABASE SYSTEM HAVING HETEROGENEOUS OBJECT TYPES may be embodied in a computer program product that includes a computer usable medium. For example, such a computer usable medium can include a readable memory device, such as a solid state memory device, a hard drive device, a CD-ROM, a DVD-ROM, or a computer diskette, having stored computer-readable program code segments. The computer readable medium can also include a communications or transmission medium, such as a bus or a communications link, either optical, wired, or wireless, carrying program code segments as digital or analog data signals. 
   While this system has been particularly shown and described with references to particular embodiments, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the invention encompassed by the appended claims. For example, the methods of the invention can be applied to various environments, and are not limited to the described environment.