2 Spatial Data Types and Metadata

2.2.1 SDO_GTYPE

The SDO_GTYPE attribute indicates the type of the geometry. Valid geometry types correspond to those specified in the Geometry Object Model for the OGIS Simple Features for SQL specification (with the exception of Surfaces). The numeric values differ from those given in the OGIS specification, but there is a direct correspondence between the names and semantics where applicable.

The SDO_GTYPE value is 4 digits in the format dltt, where:

• d identifies the number of dimensions (2, 3, or 4)

• l identifies the linear referencing measure dimension for a three-dimensional linear referencing system (LRS) geometry, that is, which dimension (3 or 4) contains the measure value. For a non-LRS geometry, or to accept the Spatial default of the last dimension as the measure for an LRS geometry, specify 0. For information about the linear referencing system (LRS), see Chapter 7.

• tt identifies the geometry type (00 through 07, with 08 through 99 reserved for future use).

Table 2-1 shows the valid SDO_GTYPE values. The Geometry Type and Description values reflect the OGIS specification.

The d in the Value column of Table 2-1 is the number of dimensions: 2, 3, or 4. For example, an SDO_GTYPE value of 2003 indicates a two-dimensional polygon.

The number of dimensions reflects the number of ordinates used to represent each vertex (for example, X,Y for two-dimensional objects). Points and lines are considered two-dimensional objects. (However, see Section 7.2 for dimension information about LRS points.)

In any given layer (column), all geometries must have the same number of dimensions. For example, you cannot mix two-dimensional and three-dimensional data in the same layer.

The following methods are available for returning the individual dltt components of the SDO_GTYPE for a geometry object: GET_DIMS, GET_LRS_DIM, and GET_GTYPE. These methods are described in Chapter 11.

2.2.2 SDO_SRID

The SDO_SRID attribute can be used to identify a coordinate system (spatial reference system) to be associated with the geometry. If SDO_SRID is null, no coordinate system is associated with the geometry. If SDO_SRID is not null, it must contain a value from the SRID column of the MDSYS.CS_SRS table (described in Section 6.4.1), and this value must be inserted into the SRID column of the USER_SDO_GEOM_METADATA view (described in Section 2.4).

All geometries in a geometry column must have the same SDO_SRID value.

For information about coordinate systems, see Chapter 6.

2.2.3 SDO_POINT

The SDO_POINT attribute is defined using the SDO_POINT_TYPE object type, which has the attributes X, Y, and Z, all of type NUMBER. (The SDO_POINT_TYPE definition is shown in Section 2.2.) If the SDO_ELEM_INFO and SDO_ORDINATES arrays are both null, and the SDO_POINT attribute is non-null, then the X and Y values are considered to be the coordinates for a point geometry. Otherwise, the SDO_POINT attribute is ignored by Spatial. You should store point geometries in the SDO_POINT attribute for optimal storage; and if you have only point geometries in a layer, it is strongly recommended that you store the point geometries in the SDO_POINT attribute.

Section 2.3.5 illustrates a point geometry and provides examples of inserting and querying point geometries.

2.2.4 SDO_ELEM_INFO

The SDO_ELEM_INFO attribute is defined using a varying length array of numbers. This attribute lets you know how to interpret the ordinates stored in the SDO_ORDINATES attribute (described in Section 2.2.5).

Each triplet set of numbers is interpreted as follows:

• SDO_STARTING_OFFSET -- Indicates the offset within the SDO_ORDINATES array where the first ordinate for this element is stored. Offset values start at 1 and not at 0. Thus, the first ordinate for the first element will be at SDO_GEOMETRY.SDO_ORDINATES(1). If there is a second element, its first ordinate will be at SDO_GEOMETRY.SDO_ORDINATES(n), where n reflects the position within the SDO_ORDINATE_ARRAY definition (for example, 19 for the 19th number, as in Figure 2-3 later in this chapter).

• SDO_ETYPE -- Indicates the type of the element. Valid values are shown in Table 2-2.

  SDO_ETYPE values 1, 2, 1003, and 2003 are considered simple elements. They are defined by a single triplet entry in the SDO_ELEM_INFO array. For SDO_ETYPE values 1003 and 2003, the first digit indicates exterior (1) or interior (2):

  1003: exterior polygon ring (must be specified in counterclockwise order)

  2003: interior polygon ring (must be specified in clockwise order)

  
  

  Note: The use of 3 as an SDO_ETYPE value for polygon ring elements in a single geometry is discouraged. You should specify 3 only if you do not know if the simple polygon is exterior or interior, and you should then upgrade the table or layer to the current format using the SDO_MIGRATE.TO_CURRENT procedure, described in Chapter 17. You cannot mix 1-digit and 4-digit SDO_ETYPE values in a single geometry. If you use 4-digit SDO_ETYPE values, you must use 4-digit SDO_GTYPE values.

  
  

  SDO_ETYPE values 4, 1005, and 2005 are considered compound elements. They contain at least one header triplet with a series of triplet values that belong to the compound element. For SDO_ETYPE values 1005 and 2005, the first digit indicates exterior (1) or interior (2):

  1005: exterior polygon ring (must be specified in counterclockwise order)

  2005: interior polygon ring (must be specified in clockwise order)

  
  

  Note: The use of 5 as an SDO_ETYPE value for polygon ring elements in a single geometry is discouraged. You should specify 5 only if you do not know if the compound polygon is exterior or interior, and you should then upgrade the table or layer to the current format using the SDO_MIGRATE.TO_CURRENT procedure, described in Chapter 17. You cannot mix 1-digit and 4-digit SDO_ETYPE values in a single geometry. If you use 4-digit SDO_ETYPE values, you must use 4-digit SDO_GTYPE values.

  
  

  The elements of a compound element are contiguous. The last point of a subelement in a compound element is the first point of the next subelement. The point is not repeated.

• SDO_INTERPRETATION -- Means one of two things, depending on whether or not SDO_ETYPE is a compound element.

  If SDO_ETYPE is a compound element (4, 1005, or 2005), this field specifies how many subsequent triplet values are part of the element.

  If the SDO_ETYPE is not a compound element (1, 2, 1003, or 2003), the interpretation attribute determines how the sequence of ordinates for this element is interpreted. For example, a line string or polygon boundary may be made up of a sequence of connected straight line segments or circular arcs.

  Descriptions of valid SDO_ETYPE and SDO_INTERPRETATION value pairs are given in Table 2-2.

If a geometry consists of more than one element, then the last ordinate for an element is always one less than the starting offset for the next element. The last element in the geometry is described by the ordinates from its starting offset to the end of the SDO_ORDINATES varying length array.

For compound elements (SDO_ETYPE values 4, 1005, or 2005), a set of n triplets (one for each subelement) is used to describe the element. It is important to remember that subelements of a compound element are contiguous. The last point of a subelement is the first point of the next subelement. For subelements 1 through n-1, the end point of one subelement is the same as the starting point of the next subelement. The starting point for subelements 2...n-2 is the same as the end point of subelement 1...n-1. The last ordinate of subelement n is either the starting offset minus 1 of the next element in the geometry, or the last ordinate in the SDO_ORDINATES varying length array.

The current size of a varying length array can be determined by using the function varray_variable.Count in PL/SQL or OCICollSize in the Oracle Call Interface (OCI).

The semantics of each SDO_ETYPE element and the relationship between the SDO_ELEM_INFO and SDO_ORDINATES varying length arrays for each of these SDO_ETYPE elements are given in Table 2-2.

2.2.5 SDO_ORDINATES

The SDO_ORDINATES attribute is defined using a varying length array (1048576) of NUMBER type that stores the coordinate values that make up the boundary of a spatial object. This array must always be used in conjunction with the SDO_ELEM_INFO varying length array. The values in the array are ordered by dimension. For example, a polygon whose boundary has four two-dimensional points is stored as {X1, Y1, X2, Y2, X3, Y3, X4, Y4, X1, Y1}. If the points are three-dimensional, then they are stored as {X1, Y1, Z1, X2, Y2, Z2, X3, Y3, Z3, X4, Y4, Z4, X1, Y1, Z1}. Spatial index creation, operators, and functions ignore the Z values because this release of the product supports only two-dimensional spatial objects. The number of dimensions associated with each point is stored as metadata in the xxx_SDO_GEOM_METADATA views, described in Section 2.4.

The values in the SDO_ORDINATES array must all be valid and non-null. There are no special values used to delimit elements in a multielement geometry. The start and end points for the sequence describing a specific element are determined by the STARTING_OFFSET values for that element and the next element in the SDO_ELEM_INFO array, as explained previously. The offset values start at 1. SDO_ORDINATES(1) is the first ordinate of the first point of the first element.

2.2.6 Usage Considerations

You should use the SDO_GTYPE values as shown in Table 2-1; however, Spatial does not check or enforce all geometry consistency constraints. Spatial does check the following:

• For SDO_GTYPE values d001 and d005, any subelement not of SDO_ETYPE 1 is ignored.

• For SDO_GTYPE values d002 and d006, any subelement not of SDO_ETYPE 2 or 4 is ignored.

• For SDO_GTYPE values d003 and d007, any subelement not of SDO_ETYPE 3 or 5 is ignored. (This includes SDO_ETYPE variants 1003, 2003, 1005, and 2005, which are explained in Section 2.2.4).

The SDO_GEOM.VALIDATE_GEOMETRY_WITH_CONTEXT function can be used to evaluate the consistency of a single geometry object or of all geometry objects in a specified feature table.

2.3.1 Rectangle

Figure 2-2 illustrates the rectangle that represents cola_a in the example in Section 2.1.

Figure 2-2 Rectangle

Description of the illustration rectangle.gif

In the SDO_GEOMETRY definition of the geometry illustrated in Figure 2-2:

• SDO_GTYPE = 2003. The 2 indicates two-dimensional, and the 3 indicates a polygon.

• SDO_SRID = NULL.

• SDO_POINT = NULL.

• SDO_ELEM_INFO = (1, 1003, 3). The final 3 in 1,1003,3 indicates that this is a rectangle. Because it is a rectangle, only two ordinates are specified in SDO_ORDINATES (lower-left and upper-right).

• SDO_ORDINATES = (1,1, 5,7). These identify the lower-left and upper-right ordinates of the rectangle.

Example 2-2 shows a SQL statement that inserts the geometry illustrated in Figure 2-2 into the database.

INSERT INTO cola_markets VALUES(
  1,
  'cola_a',
  SDO_GEOMETRY(
    2003,  -- two-dimensional polygon
    NULL,
    NULL,
    SDO_ELEM_INFO_ARRAY(1,1003,3), -- one rectangle (1003 = exterior)
    SDO_ORDINATE_ARRAY(1,1, 5,7) -- only 2 points needed to
          -- define rectangle (lower left and upper right) with
          -- Cartesian-coordinate data
  )
);

2.3.2 Polygon with a Hole

Figure 2-3 illustrates a polygon consisting of two elements: an exterior polygon ring and an interior polygon ring. The inner element in this example is treated as a void (a hole).

Figure 2-3 Polygon with a Hole

Description of the illustration poly_hole.gif

In the SDO_GEOMETRY definition of the geometry illustrated in Figure 2-3:

• SDO_GTYPE = 2003. The 2 indicates two-dimensional, and the 3 indicates a polygon.

• SDO_SRID = NULL.

• SDO_POINT = NULL.

• SDO_ELEM_INFO = (1,1003,1, 19,2003,1). There are two triplet elements: 1,1003,1 and 19,2003,1.

  1003 indicates that the element is an exterior polygon ring; 2003 indicates that the element is an interior polygon ring.

  19 indicates that the second element (the interior polygon ring) ordinate specification starts at the 19th number in the SDO_ORDINATES array (that is, 7, meaning that the first point is 7,5).

• SDO_ORDINATES = (2,4, 4,3, 10,3, 13,5, 13,9, 11,13, 5,13, 2,11, 2,4,
  7,5, 7,10, 10,10, 10,5, 7,5).

• The area (SDO_GEOM.SDO_AREA function) of the polygon is the area of the exterior polygon minus the area of the interior polygon. In this example, the area is 84 (99 - 15).

• The perimeter (SDO_GEOM.SDO_LENGTH function) of the polygon is the perimeter of the exterior polygon plus the perimeter of the interior polygon. In this example, the perimeter is 52.9193065 (36.9193065 + 16).

Example 2-3 shows a SQL statement that inserts the geometry illustrated in Figure 2-3 into the database.

INSERT INTO cola_markets VALUES(
  10,
  'polygon_with_hole',
  SDO_GEOMETRY(
    2003,  -- two-dimensional polygon
    NULL,
    NULL,
    SDO_ELEM_INFO_ARRAY(1,1003,1, 19,2003,1), -- polygon with hole
    SDO_ORDINATE_ARRAY(2,4, 4,3, 10,3, 13,5, 13,9, 11,13, 5,13, 2,11, 2,4,
        7,5, 7,10, 10,10, 10,5, 7,5)
  )
);

• Polygon A (one interior "hole"): exterior ring A0, interior ring A1

• Polygon B (two interior "holes"): exterior ring B0, interior ring B1, interior ring B2

The elements in SDO_ELEM_INFO and SDO_ORDINATES must be in one of the following orders (depending on whether you specify Polygon A or Polygon B first):

• A0, A1; B0, B1, B2

• B0, B1, B2; A0, A1

2.3.3 Compound Line String

Figure 2-4 illustrates a crescent-shaped object represented as a compound line string made up of one straight line segment and one circular arc. Four points are required to represent this shape: points (10,10) and (10,14) describe the straight line segment, and points (10,14), (6,10), and (14,10) describe the circular arc.

Figure 2-4 Compound Line String

Description of the illustration compound_line_string.gif

In the SDO_GEOMETRY definition of the geometry illustrated in Figure 2-4:

• SDO_GTYPE = 2002. The first 2 indicates two-dimensional, and the second 2 indicates one or more line segments.

• SDO_SRID = NULL.

• SDO_POINT = NULL.

• SDO_ELEM_INFO = (1,4,2, 1,2,1, 3,2,2). There are three triplet elements: 1,4,2, 1,2,1, and 3,2,2.

  The first triplet indicates that this element is a compound line string made up of two subelement line strings, which are described with the next two triplets.

  The second triplet indicates that the line string is made up of straight line segments and that the ordinates for this line string start at offset 1. The end point of this line string is determined by the starting offset of the second line string, 3 in this instance.

  The third triplet indicates that the second line string is made up of circular arcs with ordinates starting at offset 3. The end point of this line string is determined by the starting offset of the next element or the current length of the SDO_ORDINATES array, if this is the last element.

• SDO_ORDINATES = (10,10, 10,14, 6,10, 14,10).

Example 2-4 shows a SQL statement that inserts the geometry illustrated in Figure 2-4 into the database.

INSERT INTO cola_markets VALUES(
  11,
  'compound_line_string',
  SDO_GEOMETRY(
    2002,
    NULL,
    NULL,
    SDO_ELEM_INFO_ARRAY(1,4,2, 1,2,1, 3,2,2), -- compound line string
    SDO_ORDINATE_ARRAY(10,10, 10,14, 6,10, 14,10)
  )
);

2.3.4 Compound Polygon

Figure 2-5 illustrates an ice cream cone-shaped object represented as a compound polygon made up of one straight line segment and one circular arc. Five points are required to represent this shape: points (6,10), (10,1), and (14,10) describe one acute angle-shaped line string, and points (14,10), (10,14), and (6,10) describe the circular arc. The starting point of the line string and the ending point of the circular arc are the same point (6,10). The SDO_ELEM_INFO array contains three triplets for this compound line string. These triplets are {(1,1005,2), (1,2,1), (5,2,2)}.

Figure 2-5 Compound Polygon

Description of the illustration compound_polygon.gif

In the SDO_GEOMETRY definition of the geometry illustrated in Figure 2-5:

• SDO_GTYPE = 2003. The 2 indicates two-dimensional, and the 3 indicates a polygon.

• SDO_SRID = NULL.

• SDO_POINT = NULL.

• SDO_ELEM_INFO = (1,1005,2, 1,2,1, 5,2,2). There are three triplet elements: 1,1005,2, 1,2,1, and 5,2,2.

  The first triplet indicates that this element is a compound polygon made up of two subelement line strings, which are described using the next two triplets.

  The second triplet indicates that the first subelement line string is made up of straight line segments and that the ordinates for this line string start at offset 1. The end point of this line string is determined by the starting offset of the second line string, 5 in this instance. Because the vertices are two-dimensional, the coordinates for the end point of the first line string are at ordinates 5 and 6.

  The third triplet indicates that the second subelement line string is made up of a circular arc with ordinates starting at offset 5. The end point of this line string is determined by the starting offset of the next element or the current length of the SDO_ORDINATES array, if this is the last element.

• SDO_ORDINATES = (6,10, 10,1, 14,10, 10,14, 6,10).

Example 2-5 shows a SQL statement that inserts the geometry illustrated in Figure 2-5 into the database.

INSERT INTO cola_markets VALUES(
  12,
  'compound_polygon',
  SDO_GEOMETRY(
    2003,  -- two-dimensional polygon
    NULL,
    NULL,
    SDO_ELEM_INFO_ARRAY(1,1005,2, 1,2,1, 5,2,2), -- compound polygon
    SDO_ORDINATE_ARRAY(6,10, 10,1, 14,10, 10,14, 6,10)
  )
);

2.3.5 Point

Figure 2-6 illustrates a point-only geometry at coordinates (12,14).

Figure 2-6 Point-Only Geometry

Description of the illustration point_only.gif

In the SDO_GEOMETRY definition of the geometry illustrated in Figure 2-6:

• SDO_GTYPE = 2001. The 2 indicates two-dimensional, and the 1 indicates a single point.

• SDO_SRID = NULL.

• SDO_POINT = SDO_POINT_TYPE(12, 14, NULL). The SDO_POINT attribute is defined using the SDO_POINT_TYPE object type, because this is a point-only geometry.

  For more information about the SDO_POINT attribute, see Section 2.2.3.

• SDO_ELEM_INFO and SDO_ORDINATES are both NULL, as required if the SDO_POINT attribute is specified.

Example 2-6 shows a SQL statement that inserts the geometry illustrated in Figure 2-6 into the database.

INSERT INTO cola_markets VALUES(
   90,
   'point_only',
   SDO_GEOMETRY(
      2001,
      NULL,
      SDO_POINT_TYPE(12, 14, NULL),
      NULL,
      NULL));

You can search for point-only geometries based on the X, Y, and Z values in the SDO_POINT_TYPE specification. Example 2-7 is a query that asks for all points whose first coordinate (the X value) is 12, and it finds the point that was inserted in Example 2-6.

SELECT * from cola_markets c WHERE c.shape.SDO_POINT.X = 12;

    MKT_ID NAME                                                                
---------- --------------------------------                                     
SHAPE(SDO_GTYPE, SDO_SRID, SDO_POINT(X, Y, Z), SDO_ELEM_INFO, SDO_ORDINATES)    
--------------------------------------------------------------------------------
        90 point_only                                                           
SDO_GEOMETRY(2001, NULL, SDO_POINT_TYPE(12, 14, NULL), NULL, NULL)

2.3.6 Type 0 (Zero) Element

Type 0 (zero) elements are used to model geometry types that are not supported by Oracle Spatial, such as curves and splines. A type 0 element has an SDO_ETYPE value of 0. (See Section 2.2.4 for information about the SDO_ETYPE.) Type 0 elements are not indexed by Oracle Spatial, and they are ignored by Spatial functions and procedures.

Geometries with type 0 elements must contain at least one nonzero element, that is, an element with an SDO_ETYPE value that is not 0. The nonzero element should be an approximation of the unsupported geometry, and therefore it must have both:

• An SDO_ETYPE value associated with a geometry type supported by Spatial

• An SDO_INTERPRETATION value that is valid for the SDO_ETYPE value (see Table 2-2)

  (The SDO_INTERPRETATION value for the type 0 element can be any numeric value, and applications are responsible for determining the validity and significance of the value.)

The nonzero element is indexed by Spatial, and it will be returned by the spatial index.

The SDO_GTYPE value for a geometry containing a type 0 element must be set to the value for the geometry type of the nonzero element.

Figure 2-7 shows a geometry with two elements: a curve (unsupported geometry) and a rectangle (the nonzero element) that approximates the curve. The curve looks like the letter S, and the rectangle is represented by the dashed line.

Figure 2-7 Geometry with Type 0 (Zero) Element

Description of the illustration type0.gif

In the example shown in Figure 2-7:

• The SDO_GTYPE value for the geometry is 2003 (for a two-dimensional polygon).

• The SDO_ELEM_INFO array contains two triplets for this compound line string. For example, the triplets might be {(1,0,57), (11,1003,3)}. That is:

  Ordinate Starting Offset (SDO_STARTING_OFFSET)	Element Type (SDO_ETYPE)	Interpretation (SDO_INTERPRETATION)
  1	0	57
  11	1003	3

  
  

In this example:

• The type 0 element has an SDO_ETYPE value of 0.

• The nonzero element (rectangle) has an SDO_ETYPE value of 1003, indicating an exterior polygon ring.

• The nonzero element has an SDO_STARTING_OFFSET value of 11 because ordinate x6 is the eleventh ordinate in the geometry.

• The type 0 element has an SDO_INTERPRETATION value whose significance is application-specific. In this example, the SDO_INTERPRETATION value is 57.

• The nonzero element has an SDO_INTERPRETATION value that is valid for the SDO_ETYPE of 1003. In this example, the SDO_INTERPRETATION value is 3, indicating a rectangle defined by two points (lower-left and upper-right).

Example 2-8 shows a SQL statement that inserts the geometry with a type 0 element (similar to the geometry illustrated in Figure 2-7) into the database. In the SDO_ORDINATE_ARRAY structure, the curve is defined by points (6,6), (12,6), (9,8), (6,10), and (12,10), and the rectangle is defined by points (6,4) and (12,12).

INSERT INTO cola_markets VALUES(
  13,
  'type_zero_element_geom',
  SDO_GEOMETRY(
    2003,  -- two-dimensional polygon
    NULL,
    NULL,
    SDO_ELEM_INFO_ARRAY(1,0,57, 11,1003,3), -- 1st is type 0 element
    SDO_ORDINATE_ARRAY(6,6, 12,6, 9,8, 6,10, 12,10, 6,4, 12,12)
  )
);

2.4.1 TABLE_NAME

The TABLE_NAME column contains the name of a feature table, such as COLA_MARKETS, that has a column of type SDO_GEOMETRY.

The table name is stored in the spatial metadata views in all uppercase characters.

The table name cannot contain spaces or mixed-case letters in a quoted string when inserted into the USER_SDO_GEOM_METADATA view, and it cannot be in a quoted string when used in a query (unless it is in all uppercase characters).

The spatial feature table cannot be an index-organized table if you plan to create a spatial index on the spatial column.

2.4.2 COLUMN_NAME

The COLUMN_NAME column contains the name of the column of type SDO_GEOMETRY. For the COLA_MARKETS table, this column is called SHAPE.

The column name is stored in the spatial metadata views in all uppercase characters.

The column name cannot contain spaces or mixed-case letters in a quoted string when inserted into the USER_SDO_GEOM_METADATA view, and it cannot be in a quoted string when used in a query (unless it is in all uppercase characters).

2.4.3 DIMINFO

The DIMINFO column is a varying length array of an object type, ordered by dimension, and has one entry for each dimension. The SDO_DIM_ARRAY type is defined as follows:

Create Type SDO_DIM_ARRAY as VARRAY(4) of SDO_DIM_ELEMENT; 

The SDO_DIM_ELEMENT type is defined as:

Create Type SDO_DIM_ELEMENT as OBJECT (
  SDO_DIMNAME VARCHAR2(64),
  SDO_LB NUMBER,
  SDO_UB NUMBER,
  SDO_TOLERANCE NUMBER);

The SDO_DIM_ARRAY instance is of size n if there are n dimensions. That is, DIMINFO contains 2 SDO_DIM_ELEMENT instances for two-dimensional geometries, 3 instances for three-dimensional geometries, and 4 instances for four-dimensional geometries. Each SDO_DIM_ELEMENT instance in the array must have valid (not null) values for the SDO_LB, SDO_UB, and SDO_TOLERANCE attributes.

For an explanation of tolerance and how to determine the appropriate SDO_TOLERANCE value, see Section 1.5.5, especially Section 1.5.5.1.

Spatial assumes that the varying length array is ordered by dimension. The DIMINFO varying length array must be ordered by dimension in the same way the ordinates for the points in SDO_ORDINATES varying length array are ordered. For example, if the SDO_ORDINATES varying length array contains {X1, Y1, ..., Xn, Yn}, then the first DIMINFO entry must define the X dimension and the second DIMINFO entry must define the Y dimension.

Example 2-1 in Section 2.1 shows the use of the SDO_GEOMETRY and SDO_DIM_ARRAY types. This example demonstrates how geometry objects (hypothetical market areas for colas) are represented, and how the COLA_MARKETS feature table and the USER_SDO_GEOM_METADATA view are populated with the data for those objects.

2.4.4 SRID

The SRID column should contain either of the following: the SRID value for the coordinate system for all geometries in the column, or NULL if no specific coordinate system should be associated with the geometries. (For information about coordinate systems, see Chapter 6.)

2.5.1 Spatial Index Views

There are two sets of spatial index metadata views for each schema (user): xxx_SDO_INDEX_INFO and xxx_SDO_INDEX_METADATA, where xxx can be USER or ALL. These views are read-only to users; they are created and maintained by the Spatial indexing routines.

2.5.2 Spatial Index Table Definition

For an R-tree index, a spatial index table (each SDO_INDEX_TABLE entry as described in Table 2-4 in Section 2.5.1) contains the columns shown in Table 2-5.

2.5.3 R-Tree Index Sequence Object

Each R-tree spatial index table has an associated sequence object (SDO_RTREE_SEQ_NAME in the USER_SDO_INDEX_METADATA view, described in Table 2-4 in Section 2.5.1.2). The sequence is used to ensure that simultaneous updates can be performed to the index by multiple concurrent users.

The sequence name is the index table name with the letter S replacing the letter T before the underscore (for example, the sequence object MDRS_5C01$ is associated with the index table MDRT_5C01$).