JPH01144120A - Searching device for hierarchical network route - Google Patents

Abstract

PURPOSE:To search a hierarchical network route at a high speed by storing the attribute information on a weight slot showing the priority degrees of the frames showing paths into these frames. CONSTITUTION:A searching device for hierarchical network route includes a network route searching mechanism 110, a working memory part 111, and a route searching mechanism 112. A slot is added to divide the paths on a network into >=2 hierarchical classes in response to the priority degrees of these paths and to store the division of the classes of paths into the network connecting information expressing frames 140, together with a slot, e.g., a WEIGHT slot 200 which stores the attribute values of paths themselves and shows the priority degrees of said attribute values. When a route to be extended next is selected among plural routes under evolution, the value of evaluation is calculated from the attribute values of paths forming each route and the division of classes. Based on said value of evaluation, the paths of higher priority degrees are evolved with preference for acquisition of a route between two nodes. Thus a route searching system is attained with high efficiency.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a hierarchical network route search device that can be applied to the problem of searching for the shortest route in a network consisting of nodes and paths such as roads, and that can search at high speed. It is related to.

(Prior Art) The problem of searching for the shortest route between two different nodes in a network composed of nodes and paths often appears in our daily life. An example of this problem is finding the shortest route from one point to another in a metropolitan metropolitan subway system. There has already been some research on algorithms that search for this shortest route, such as Win
ton, translated by Nagao et al., "Artificial Intelligence" (Baifukan), 4.
Section 1 ``Basic Search J (pp, 99-101) is detailed.

The components of a network are nodes and paths.

In FIG. 6, 1 indicates a node. Here, A, B
etc. are node names, and in a subway network, a station corresponds to a node. 2 is a path, which in a subway network is a track between two adjacent stations. Hereinafter, in this specification, the path between AB will be treated as the name rA BJ. FIG. 6 shows the length of each path as a subway network. In order to find the shortest route, it is desirable that the sum of the lengths of the paths that make up this route be the minimum. In this specification, the attributes unique to each path, which are the basis for calculating evaluation values for route selection, are referred to as "attribute values."

The shortest route of the network shown in FIG. 6 is determined as follows. However, suppose we are looking for a route between A and H, and the search starts from A. The route is extended from A, and if there is a branch at a node, the route is also extended while branching into a plurality of nodes. In this specification, the tip node of the currently extended route is referred to as a "frontier." During a search, there are usually multiple frontiers. When the frontier reaches the terminal (H in Figure 6), and the extension distances of all other routes that have not reached the frontier are greater than the routes that have reached the terminal, the search ends. The route that reaches the terminal is the shortest path required.

In Fig. 7, routes under development are shown as ■~■. In this case, the hatched node (E.

F, D) becomes the frontier.

The conventional algorithm is as follows.

(1) Among all routes with frontiers, select the route with the minimum length (total of attribute values of paths composing the route), and set this as R and the frontier of R as F.

(2) For each path connecting to node F, branch and extend the route, and add the node (opposite to F) of each path to the frontier set. Delete old Frontier F from the Frontier set. The length of each path plus the length of R is the extension of each new route. However, at the time of the "frontier end", it is included in the frontier set, but it is not included in the subsequent extension, and its evaluation value is stored as the evaluation value of the provisional solution (route).

(3) If no route has reached the terminal, return to (1). Otherwise, jump to (4).

(4) If the extension distances of all other routes that have not reached the frontier are greater than the route that has reached the terminal, go to (5). Otherwise (1)
Return to

(5) End However, if the route being searched by the above algorithm merges with another route, it is necessary to give priority to the route with the smaller evaluation value and stop developing the route with the larger evaluation value.

The specific steps will be explained with reference to FIG. However, F
L represents the set of frontiers, and R3 represents the set of routes being searched. (A B) is a symbol representing a list consisting of A and B, and is used to represent a set consisting of list elements. NIL indicates nothing. (A B
C, 5) represents a route from A to C via B, and the last "5" is the evaluation value (here, length) of this route. Note that S1 to Sf indicate each step.

Let SO,A be the starting point of the search.

FL ← (A) R3 ← NIL Sl, A to B and C heir route extension FL ← (B C) RS ← ((A B 3) (A C2)) 2 routes (A B) (A C), evaluation The smaller value (A C) is extended next.

S2. C to E and D herot extension FL←(B E D) R3-((A B 3) (A CE 5)(
A CD 5)) For example, the evaluation value of (A CE) is 2Km of A, C and C
E is a total of 3km.

Among the three routes (A B) (A CE) (A CD), the one with the smallest evaluation value (A B) is extended next.

S3. B to E and F herot extension FL ← (E F D) RS ← ((A B E 5) (A C
E 5) (A B F 6) (A
CD 5)) Here, there are two routes with E as the frontier, and their evaluation values are the same, so randomly choose (A
CE 5) will be deleted.

Since the two routes (A B E) and (A CD) have the same evaluation value, (A CD) is randomly selected as the next development candidate.

S4. FL-(EFH) R3-((A B E 5)(A B F
6) (A CD H9)) Since terminal H has been reached, the tentative solution candidate is (ACD H
). Its evaluation value is 9.

Other routes in progress (A B E 5) (AB
The minimum evaluation value of F6) is 5, which is smaller than the evaluation value of 9 for the provisional solution, so we continue to develop the route. The underlined routes reach the terminal node and are not subject to extension.

Among the three routes, the one with the smallest evaluation value (A BE 5
) as the next expansion candidate.

S5. Extend the E to F to G her route. Here, the route from E to C is known to be far away, so it is not expanded.

FL←(F G H) RS←((A B E F 7) (A B
a6) (A B F 6) (A CD H
dan)) Here, there are two routes with F as the frontier, and the one with the highest evaluation value (A B E F7) is deleted. Since the evaluation value of the route being developed is less than 9, the search continues.

2 routes (A B E G) (A B F)
Since the evaluation values are the same, (A B F) is randomly selected as the next development candidate.

S6. Extend the H root from F.

FL←(GH) RS←((A B E G 6) (A B
FH9) (A CD H9)) Since the evaluation value of the route being developed is less than 9, the search continues.

A route with an evaluation value smaller than the evaluation value 9 of the provisional solution is (
A B E G) only.

S7. FL ← (H) which extends the route from G to H. The frontier is only H, and the route with the minimum extension is (
A B E G H).

[End of search]

In the existing algorithm described above, root expansion is performed seven times.

FIG. 8 shows a conventional network route searching device. 10 is a network route search mechanism, which is composed of a working memory section 11 and a search mechanism 12. The working memory unit 11 is realized in a format well known as "r frame" in the field of artificial intelligence technology, and includes a frame 30 representing each node and a frame 40 representing each path.
is held. 31 is the name of the frame, and here the name of the frame, that is, the node name is "C". A frame 30 corresponding to each node is called an "instance" belonging to the "r node class", and a class frame 20 representing a class is placed above the instance frame 30, and between the class frame 20 and the instance frame 30. are connected by pointers. There are also frames 40 representing a plurality of paths under the path class frame 21.

Each frame is provided with storage locations 32 called slots. In frame “A” of FIG. 8, rPAT)IJ
There are two types of slots rROUTEJ, and the value 33 of the slot is ``(AB BC)J r
(A O)J is memorized.

The meaning of each slot in the example of FIG. 8 will be clear. In other words, the current state is when route expansion starts from A, and node frame A is connected to r node A by AB and A.
There are two paths of C, the only root being r (A)J, and its evaluation value is "0". It shows one thing. In the C frame, the route being expanded is (A C)
So, its evaluation value is 2. Reference numeral 12 denotes a search mechanism, which includes a frontier list storage area 55 that stores where the current frame is located, and a shortest route detection unit that reads the frontier from the frontier list storage area 55 using a data access path 54 and detects the route with the minimum evaluation value. and a next path expansion mechanism 50 that expands the next route based on the output result 52 of the shortest route detection mechanism 53. 60 and 61 are data transfer paths between the search mechanism 12 and the working memory unit 11. Further, 51 is a frontier node modification instruction path from the next path expansion mechanism 50 to the frontier list storage area 55.

The operation of the network route search device shown in FIG. 8 will be clear from the explanation of the algorithm. The shortest route detection mechanism 53 accesses the node frame (in the working memory unit 11) corresponding to each frontier node name stored in the frontier list storage area 55, and extracts all the nodes stored in the rROUTEJ slot of each node. Select the route with the smallest evaluation value from among the routes. Next, the next path expansion mechanism 5o extracts the node to be expanded next from the route having the smallest evaluation value, and selects the node to be expanded from the rRATHJ slot of the node frame (in the working memory unit 11) corresponding to the node to be expanded. , select only the paths that do not retrace the route, access the path frame (in the working memory unit 11) for each path, and write ``
The length, which is the attribute value of the path, is extracted from the LENGTHJ slot. Further, based on this attribute value, new route information is generated and transferred to the node frame, and a frontier node modification instruction path 51 issues an instruction to add a new frontier and delete an old frontier.

The next pass expansion mechanism 50 will be explained in more detail.

For example, if (A C5) is the route to be expanded, path candidate AC,
CE, take out the CD, and in it, AC, which means going back.
Except for , CE and CD are the expansion paths. The next pass expansion mechanism 5o is CE.

Read from the CD frame that the lengths of the paths to be expanded are 3 and 3, respectively, and (A CE8) (A C
D 8) rRO of nodes E and D with new route
Register in UTEJ frame. Furthermore, the next path expansion mechanism 50 deletes frontier C from the frontier list storage area 55 and adds frontiers E and D in its place.

In reality, the shortest route detection mechanism 53 also needs a function to detect that the frontier has reached the end of the target, a function to store a provisional solution, and a function to compare the currently developed route with the provisional solution. Also, regarding the next path expansion mechanism 5o, when another route already exists at the node to which the route has been expanded, it is determined whether the existing route is advantageous or the currently expanded one is advantageous, and unnecessary routes are removed. (This function also eliminates the route that backtracks when expanding the route.) However, these detailed functions are not directly related to the gist of the present invention and will therefore be omitted from further explanation.

[Problem that the invention seeks to solve]

Although the conventional route search algorithm described above is mathematically simple, it has major problems when applied to real problems. First, in an actual network, it is impossible for the number of nodes to be as small as shown in FIG. Even Tokyo's subway system has dozens of stations, and the nationwide JR network has an enormous number of nodes.

In the above search algorithm, the main processing time is the processing to extend the path from the frontier and the sorting processing time to select the route with the smallest evaluation value from among multiple routes. Among these, the number of path extensions is proportional to the number of paths on the Habo network. The sorting processing time is Nr3・LoglJ of the number of frontiers (Nr),
, and N is approximately proportional to the square root of the number of nodes on the network. For this reason, as the number of nodes increases, the processing time increases rapidly, and with the current computer capabilities, it is difficult to provide the short response required by humans, even on the shortest route on the Tokyo subway.

However, do humans perform exhaustive searches like the one described above? Considering the actual road network, there are first-class national highways and back roads. When we search for a route from one point to another, it is obvious that we give priority to trunk lines. Even though there is a national highway nearby, I don't choose a route that winds through only the shopping district. In other words, a large network always has a ``main line'' and a ``branch line,'' and we unconsciously prioritize the main line when searching for routes. However, network route search devices using conventional algorithms
There is a problem in that such a highly efficient search cannot be realized.

An object of the present invention is to realize a network route search device that provides a means for distinguishing path priorities in the network search described above and enables more efficient route search similar to the human search method.

(Means for Solving the Problems) A hierarchical network route search device according to the present invention includes a working memory unit that stores connection information of a network formed from nodes and paths in a frame format, and a working memory unit that stores connection information of a network formed from nodes and paths, and a It has a route search mechanism that simultaneously deploys multiple routes between the networks and extends the route with the smallest evaluation value first, and hierarchizes the paths on the network into at least two or more classes according to their priorities. , the frame for expressing network connection information is provided with a slot for storing the class classification of the path and a slot for storing the attribute value of the path itself.

[Effect]

In this invention, when calculating the evaluation value of each route for selecting the next route to be extended from a plurality of currently developed routes, the attribute value and class classification of each path constituting each route are calculated. Evaluation values are calculated from both, and based on the evaluation values, a route with a high priority is developed preferentially to find a route between two nodes.

〔Example〕

FIG. 1 shows an embodiment of the invention. Further, in the present invention, paths on the network are hierarchically arranged according to priorities, and FIG. 4 shows an example of a network in which the paths are hierarchically arranged into two layers. The network in FIG. 4 is similar to that in FIG. 6, but the route (AB E GH) is the "main line" and all other paths are "branch lines." Here, there are two layers, but in general there may be any number of layers. Furthermore, this way of thinking of separating ``main lines'' and ``branch lines'' is natural in our daily lives. In this invention, a "weight" indicating the priority level is given corresponding to the hierarchy of the path. FIG. 5 shows a list of attribute values (specifically, lengths) and weights of the paths shown in FIG. 4. A path with a weight of 1 is a trunk line and has a high priority.

In FIG. 1, 110 is a network route search mechanism of the present invention, 111 is a working memory section, and 112 is a route search mechanism. 121 is a path class frame, 1
40 is a pass frame. 200 is a newly added r
This is the WE I GHTJ slot, and 153 is the shortest route detection mechanism.

The embodiment shown in FIG. 1 has two differences from the conventional example shown in FIG. 8, both of which are indicated by "shading" in FIG. The first is that an rWE I GHTJ slot indicating the priority is added to the path frame 140 and the weight shown in FIG. ) is used to search for the next route to be extended.

Next, a route search is executed in detail according to FIG. However, FL is a list of frontiers, and RS is a set of routes. The evaluation value is not the length of the route, but the sum of the lengths of each path multiplied by weights.

Let So, A be the starting point of the search.

FL←(A) RS-NIL Sl, A to B and C route extension FL←(B C) RS←((A B 3) (A C4)) Here, the evaluation value of the route (A B) is 3×1 , (AC)
The evaluation value is 2×2.

Among the two routes (A B) (A C), the one with the smallest evaluation value (A B) is extended next.

S2.8 to E and F herot extension FL ← (CE F) RS ← ((A B E 5) (A B F
9) (A C4)) Set the route (A C4) as the next expansion candidate.

S3. C to E and D herot extension FL←(E D F) RS←((A CD 10)(A B E
5) (A B F 9) (A CE 10)
) There are two routes with E as the frontier, but delete the route with a large evaluation value (A CE 10).

Let rule 1-(A B E 5) be the next expansion candidate.

S4. FL←(D F G) RS←((A CD 10)(A B E
F9) (A B E G 6) (A B
FHere, there are two routes with F as the frontier, and their evaluation values are the same, so randomly select (A B E
Delete F9).

Let the route (A B E G) be the next expansion candidate.

S5. Extend the H root from G.

FL←(D F H) RS←((A CD 10)(A B E
GH8) (A B F 9)) Here, (A B E GH) has reached the end and the evaluation values of the other routes are greater than 8, so the process is terminated.

[End of search]

As described above, according to this invention, the number of times the root is expanded is 5.
This is a decrease compared to 7 times in the prior art. Since the network is small, the effect of the invention is not so significant. However, as the network becomes larger, the difference in the number of searches increases, and the effect of this invention becomes more significant. Note that in this method, because the paths are weighted, the route with the minimum distance may not always be found as a solution. However, this is also a common occurrence in our daily lives. In other words, when we go far away, no matter how short the route is, if it takes a long time, we use national highways and express routes, even if it is a little detour. On the other hand, when people have time, they will choose a cheaper route even if it is a detour. By changing the weights of the paths in this way, it is possible to select not only the route with the shortest distance, but also the route that meets the user's objectives, such as the shortest time or the lowest price.

Now, in the above case, there is only one type of trunk line, so the path itself is weighted. In other words, if the path was a trunk line, the weight was 1. However, if there are several types of trunk lines and they intersect, it is necessary to change the weights among the trunk lines. Here, it is assumed that the weight of a path is not unique to the path, but is determined each time by the direction of the route expanded immediately before the path is expanded.

Next, the working memory section 111 and the route search mechanism 1
12 more detailed implementation methods are shown below.

FIG. 2(a) shows an example of implementation of the working memory section 111. The working memory section 111 includes a storage cell plane 304 and an address decoder 3o3. Address register 300. Read data register 301 for storing read information from memory cells. It is comprised of a write data register 302 that stores information written to memory cells and a control section 311 that performs overall control. 306 is an address information transfer path, 305 is a cell activation path, 307 is a write information transfer path, 308 is a read information transfer path, 309 is an address information transfer path, and 310 is a control signal transfer path.

Frame information on the working memory is stored on the storage cell brain 304 in FIG. 2(a), and as shown in FIG. 2, the frame names and addresses are associated in advance by the compiler. This correspondence is
This can be done by Compal techniques common to those skilled in the art. 320 in FIG. 2(b) is a correspondence diagram between symbols and addresses.

The meaning of FIG. 2(a) is that the frame (PATH) corresponds to address 12, and the symbol name rPATHJ of that frame is stored in the storage cell at address 12 of PATH, and from that address in the address addition direction. By reading the cells one after another, the address containing the instance rABJrACJ of the class rPATHJ is obtained.

r/ENDJ is a symbol indicating that the interface information ends there. Further, it is shown that frame rACJ includes a slot whose name includes a symbol at the 10th address and a slot whose name includes a symbol at the 11th address.

When reading the slot value using the network search system, the following operations are performed. First, frame r
Suppose you want to read slot r WHIGHTJ of AcJ. In this case, with the frame name rAcJ, the working memory section 1
11 is not accessed, but the working memory section is requested to fetch the value of the slot "slot name near address 11" of the frame stored at address 5.

A control signal is sent to the control unit 311 from the control signal transfer path 310, and a slot value reading operation is started. Read address 5 is first entered into address register 300. Further, the address corresponding to the slot name is stored in the read data register 301 for comparison. The address register 300 adds 1 to this address,
This information is transferred to address decoder 303 via address information transfer path 306. Address decoder 303 energizes this No. 6 memory cell and reads cell information to read data register 301 . Here, the content of this read data register 301 is address number 10, not address number 11 as expected. Therefore, in the address register 300, an address is created by further adding 2.

When this address No. 8 is accessed, the target address 11 is certainly stored, so the address register 300 is further incremented by 1 and the target information (in this case, 2) is read from the address No. 9 to the data register 300.
Transfer to. The reading of the slot value has been described above, but writing is also the same. Put the weapon data to be written into the write data register 302, and with the target slot value activated, write the data into the memory cell. The only difference is that it transfers .

FIG. 3 is a more detailed diagram of the route search mechanism 112.

The frontier list storage mechanism 55 includes a register 410 for storing newly added frontier node names, a memory 414 for storing the frontier list, a marshaller 412 for merging the contents of the added frontier list node and the frontier list, and checking for duplicates of frontier nodes. The frontier list includes a duplicate checker 413 for removing duplicates, and a read data buffer 411 for reading and holding the contents of the frontier list. The contents of the frontier list are transferred via transfer path 515 to marsher 412, where new frontier nodes sent from transfer path 514 are added and old frontier nodes are removed. The merge result is sent to the duplication checker 413 via the -transfer path 516, and duplicate frontier nodes are removed. The new frontier list is stored again in the memory 414 for storing frontier lists via the transfer path 517. Memory 41 for storing the frontier list
The contents of 4 are transferred to the read data buffer 4 via the transfer path 511.
11 and used by the shortest route detection mechanism 153.

The shortest route detection mechanism 153 includes an access unit 405 that accesses frames corresponding to each node in the frontier list via a transfer path 508 and reads out all routes being developed, and a route memory 4 that stores the read routes.
06. Sorter 4 that sorts the contents of root memory 406
07 and a register 409 for storing the expansion route. The route information read from the working memory is input to the access unit 405 via the transfer path 507 and stored in the route memory 406 via the transfer path 509. From among these routes, the sorter 407 uses the transfer path 510 to find the route with the smallest evaluation value. The result is stored in register 409 via transfer path 40B.

The next path expansion mechanism 50 reads the name of the frontier node to be expanded from the route information to be expanded, accesses the working memory, and reads the path connected to the node.The access mechanism 404 stores the read path information. It consists of a register 403, a route expander 4.1 that performs route expansion, and a write data register 400 that writes the generated route into a working memory. The newly generated frontier node name is
It is transferred to the frontier list storage mechanism 55 via the frontier node modification instruction path 51. Access mechanism 404
accesses the working memory section 11 by specifying the node name via the transfer path 504. As a result, the path information is read from the slot via the transfer path 503 and stored in the register 403 via the transfer path 5o6. The route expander 401 reads this path information through the transfer path 505, generates new route information, and
1 to the write data register 400. The contents of the write data register 400 are sent to the working memory section 11 via a transfer path 502.

Although the above configuration example is constructed using registers, transfer paths, etc., it is also possible for those skilled in the art to construct it according to the spirit of the present invention using a general-purpose μP (microprocessor) and a program. Further, in this specification, the priority is provided as path information, but a priority path may be given based on "ease of path selection" when passing through a node. In this case, it is equivalent to continuing on the train after getting on the train without getting off as much as possible.

As described above, the network route search device of the present invention is different from the prior art in that a frame representing a path stores attribute information indicating its priority. In other words, in the conventional network route search mechanism,
When calculating the evaluation value EV of a route, let Ll be the length of each path forming the route, EV = Σ L
... ... While the evaluation value is calculated using (1), the network route search mechanism of the present invention also uses a weighting value WI indicating the priority of each path, and EV=XL+XW+
``'''' Calculate the evaluation value as (2).The higher the priority, that is, the lower the weight, the smaller the increase in the EV value, and the route search is performed with priority given to the higher priority path. That will happen.

Note that any function may be selected for the above equation (2) as long as it has a correlation that suppresses the increase in the evaluation value of the path with a high priority, and the function form of equation (2) is This does not affect the spirit of this invention. Additionally, although this specification discusses the route in which the evaluation value becomes smaller as the better route, it is also conceivable that the search may be executed with the direction in which the evaluation value becomes larger as the better route.

However, even in this case, the purpose of this invention can be achieved regardless of which function is selected as the function for calculating the evaluation value, as long as it has a correlation that promotes an increase in the evaluation value. It's not something to change.

[Effects of the Invention] As explained above, the present invention has a working memory section that stores connection information of a network formed from nodes and paths in a frame format, and a system that simultaneously develops multiple routes between two different nodes of the network. and a route search mechanism that extends the route with the smallest evaluation value first, hierarchizes the paths on the network into at least two or more classes according to their priorities, and creates a frame for expressing the network connection information. is provided with a slot for storing the class classification of the path and a slot for storing the attribute value of the path itself, so that the search mechanism for searching for a route between the two nodes can select the next route from among the currently deployed routes. When calculating the evaluation value of each route in order to select a route that extends to Since the route between two nodes is determined by preferentially expanding paths with high priority based on the above, the time required for searching can be kept to a minimum even if the number of nodes in the network increases. Further, the present invention has the feature that it is possible to set a route giving priority to trunk lines, which is normally done by humans, and it is possible to present search solutions that are natural to humans.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the network route search device of the present invention, and FIG. 2(a) is a block diagram showing an embodiment of the network route search device of the present invention. (b) is a more detailed configuration diagram of the working memory section and the correspondence diagram between symbols and addresses, FIG. 3 is a more detailed configuration diagram of the search mechanism, FIG. 4 is a diagram showing an example of a network having a trunk line, and FIG. The figures are diagrams showing examples of weighting information used in this invention, FIG. 6 is a diagram showing an example of a network, and FIG.
This figure shows an example of a network in which frontier nodes are specified, and FIG. 8 is a diagram showing a conventional network route search device. In the figure, 5o is the next path expansion mechanism, 51 is the frontier node modification instruction path, 52 is the output result of the shortest route detection mechanism, 54 is the data access path, 55 is the frontier list storage area, 60.61 is the data transfer path, 110 is a network route search mechanism, 111 is a working memory section, 112 is a search mechanism, 121 is a path class frame,
140 is a path class frame, 153 is a shortest route detection mechanism, and 200 is a weight slot. Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] a working memory unit that stores connection information of a network formed from nodes and paths in a frame format;
It has a route search mechanism that simultaneously develops multiple routes between two different nodes of the network and extends the route with the smallest evaluation value first, and creates at least two or more paths on the network according to their priorities. The network connection information representation frame is provided with a slot for storing the class division of the path and a slot for storing the path attribute value of the path itself, and the route between the two nodes is hierarchized into classes. When calculating the evaluation value of each route in order to select the next extended route from the currently expanded multiple routes, the search mechanism uses the attribute values of each path that makes up each route and the corresponding class. A hierarchical network route searching device characterized in that an evaluation value is calculated from both of the classifications, and a route between two nodes is determined by preferentially developing a path with a high priority based on the evaluation value.